azure_webapp: Support additional config properties for stacks

[srb3]

Supported stack versions and types sometimes include things like linuxFxVersion. We do not currently have methods for checking stacks reported in this way

example

inspec> cd azure_webapp(resource_group:'test-app', name: 'testapp1')                                                                                                                                                                     
inspec> configuration.properties                                                                                                                                                                                                           
=> #<#<Class:0x0000000007320ee0>::AzureResourceProbe:0x0000000006997568                                                                                                                                                                    
 @count=77,                                                                                                                                                                                                                                
 @item=                                                                                                                                                                                                                                    
  {:numberOfWorkers=>1,                                                                                                                                                                                                                    
   :defaultDocuments=>["Default.htm", "Default.html", "Default.asp", "index.htm", "index.html", "iisstart.htm", "default.aspx", "index.php", "hostingstart.html"],                   
   :netFrameworkVersion=>"v4.0",                                                                                                                                                                                                           
   :phpVersion=>"",                                                                                                                                                                                                                        
   :pythonVersion=>"",                                                                                                                                                                                                                     
   :nodeVersion=>"",                                                                                                                                                                                                                       
   :powerShellVersion=>"",                                                                                                                                                                                                                 
   :linuxFxVersion=>"PYTHON|3.7",                                                                                                                                                                                                          
   :windowsFxVersion=>nil,                                                                                                                                                                                                                 
   :requestTracingEnabled=>false,                                                                                                                                                                                                          
   :remoteDebuggingEnabled=>false,                                                                                                                                                                                                         
   :remoteDebuggingVersion=>"VS2019",                                                                                                                                                                                                      
   :httpLoggingEnabled=>false,                                                                                                                                                                                                             
   :azureMonitorLogCategories=>nil,                                                                                                                                                                                                        
   :acrUseManagedIdentityCreds=>false,                                                                                                                                                                                                     
   :acrUserManagedIdentityID=>nil,                                                                                                                                                                                                         
   :logsDirectorySizeLimit=>35,                                                                                                                                                                                                            
   :detailedErrorLoggingEnabled=>false,                                                                                                                                                                                                    
   :publishingUsername=>"$saptest1",                                                                                                                                                                                                       
   :publishingPassword=>nil,                                                                                                                                                                                                               
   :appSettings=>nil,                                                                                                                                                                                                                      
   :azureStorageAccounts=>{},                                                                                                                                                                                                              
   :metadata=>nil,                                                                                                                                                                                                                         
   :connectionStrings=>nil,

[sa-progress]

I am looking in to this issue.