test: dev library testing based on branch name or variable

[hallvictoria]

Description

Updates for installing and testing a non-prod version of the SDK / extensions:
The build wheel will be installed and the worker E2E tests will run using the wheel if:

• The branch name follows the format of sdk/* or extensions/*
• Or the corresponding USETESTPYTHONSDK / USETESTPYTHONEXTENSIONS pipeline variables are set

This allows for the scenario where we might want to do an ad-hoc test of a non-prod library version without creating a new branch for it.

Fixes #

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