Support closer integration with other frameworks

[thrix]

As a discussion item from the recent workshop, seems it would be good to talk about how we could better integrate with various frameworks like pytest, behave, avocado, ginkgo, etc.

If we could define some generic way how these frameworks could be integrated into tmt, I do believe it would help find more use cases for tmt.

Some ideas:

• how to effectively combine metadata already present in the tests (docstrings, test names)
• how effectively extend the ^ metadata with tmt metadata for grouping of tests from various frameworks, higher level grouping in plans, etc.
• support way to execute certain tests.
• it would be great to dogfood this for Testing Farm itself, to hash out the use cases

Similar issues: https://github.com/teemtee/tmt/issues/1278

Crosslinks: https://docs.google.com/document/d/1mkyxM0U9iz7rvkxlMV_32Kkhf4R1sW49zyDugJjBBUQ/edit#bookmark=id.r2fazhmlqhot

[LecrisUT]

I believe these should be done in separate repos so that it is easier to find and contribute, without triggering the massive test-suite of tmt.

Working on the cmake integration, I do find some issues with implementing plugins for these, I will try to progress more on it. I think something very useful will be splitting up the optional dependencies into their own pyproject.toml.

https://github.com/teemtee/tmt/blob/c476703aaaf85e1bd1e3c3f22dff76598836eabc/pyproject.toml#L51-L67