Consolidate testing code into new project

[maiqbal11]

Currently there is a large amount of common testing code shared between the extensions and the core sdk. The testing code should be consolidated into a new project, in the SDK repo, so that it can be shared between these projects and so that we can also provide testing capabilities to other teams developing extensions etc.

The test helpers should be packaged as a source package.

[maiqbal11]

First step in accomplishing #2011.

[fabiocav]

Updated title and description to reflect the work to be done.

[maiqbal11]

Changes are in #2029

[jeffhollan]

@maiqbal11 what's the status of this one. Looks like stuck in Sprint 41 but still open. Hoping we can keep making progress on #2011 as well. Wondering if best path forward is to get the sub-tasks for #2011 created (including this) and lets drop in the Triaged milestone and I can help stack rank for future sprint plans to get this work across. Know you are likely working on other high-pri Python worker stuff.

[maiqbal11]

@jeffhollan, @fabiocav, this one is ready to be checked in. Waiting on a go-ahead from Fabio. I can create a work item for this one but I believe the pull request has all the information regarding its intent (#2029)? For #2011, I believe there's going to be a new owner so they would be able to decide how they want to approach it. We should be able to move #2011 to Triaged until a new owner is ready to pick it up.