Give the user a hint to add the FrankConfig.xsd reference or add it automatically

[jacodg]

Is your feature request related to a problem? Please describe. When you open a configuration that doesn't have a reference to FrankConfig.xsd you will not have code completion in VSCode and Eclipse.

Describe the solution you'd like Make it easy for the user to add it. Show a message that no reference was found on opening the file and ask the user whether the Frank!Flow should add it to the root element. The following needs to be added: xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../FrankConfig.xsd"

Describe alternatives you've considered Add it automatically when it is missing

Additional context -