Adding usePythonSrcRootInImports logic to AbstractPythonConnexionServerCodegen

[tray2100]

(#9558) This PR adds a new usePythonSrcRootInImports flag to allow a user of the generator to specify that they want the pythonSrcRoot value included in the namespaces generated. The default value of false leaves the output as is today. I added this change into the AbstractPythonConnexionServerCodegen so all the extending generators can benefit from it.

I've added a new unit test suite against the AbstractPythonConnexionServerCodegen since one didn't exist. In there I use a dataProvider to test that with the new flag off that there are no changes to what is generated now and that with the flag on the appropriate paths for file generation and import namespaces are changed.

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cc: @taxpon @frol @mbohlool @cbornet @kenjones-cisco @tomplus @Jyhess @arun-nalla @spacether

[tray2100]

Oops! I didn't make the tests that check a "path" platform agnostic. I'm force pushing a consolidated commit with this fix to make this easier to merge.

[tray2100]

The tests failures seem to be unrelated to my change since they're occurring in the csharp suite and I never made any changes to the Petstore example.

[spacether]

This looks good; thank you for your PR!