Allow overriding $PROFILE file in Chocolatey installer

[tylerszabo]

System Details

• posh-git version/path: 0.7.3.1 C:\tools\poshgit\dahlbyk-posh-git-9bda399\src
• PowerShell version: 5.1.17134.112
• git version 2.18.0.windows.1
• OS: Microsoft Windows NT 10.0.17134.0

Issue Description

I notice in chocolateyInstall.ps1 for the posh-git Chocolatey package. That the install script uses the following:

    if ($PROFILE -and (Test-Path $PROFILE)) {
        Write-Verbose "Updating posh-git location in `'$PROFILE`'."
        $oldProfile = @(Get-Content $PROFILE)

It'd be really handy to be able to use Chocolatey package parameters or an Environment variable.

[dahlbyk]

Would you like to specify an exact path, or one of the named $PROFILE locations (CurrentUserAllHosts, etc)?

[tylerszabo]

In my case the exact path would be more useful since I split my profile up a bit so I'd point posh-git to $env:USERPROFILE\Documents\WindowsPowerShell\Profile_PoshGit.ps1.

[dahlbyk]

Interesting. Supporting an environment variable to override the posh-git install location seems the easiest option to let the setting propagate all the way down into Add-PoshGitToPrompt.