Improve time to run E2E tests

[tanya-borisova]

Description

As a TRE Developer
I want to bring down time it takes to run E2E tests
So that I can ship features faster

Currently, the tests take between 1hr45min and 2hrs to run. This can be significantly reduced if the tests are ran in parallel, and only relevant paths of the code base are tested.

Acceptance criteria

• Create one set of test workspaces for all E2E tests #2839
• Execute E2E tests in parallel #2840
• Session fixtures don't have effect with pytest-xdist #2868