WIP: Moving the datalad interface and test here

[yibeichan]

1. rename TODO with datalad
2. add datalad to .toml
3. update Readme
4. add git-annex to GA workflow

[yibeichan]

@djarecka please ignore this PR; I'll let you know when I'm done with moving the datalad interface here.

[yibeichan]

@djarecka as expected, got some errors...

1. i added pydra-datalad[test] to dev see here, trying to follow the logic from pydra-fsl, then I messed up all devcheck, without this line, the devcheck was okay.
2. the reason I added this to dev was because i kept getting this error in the test check: /inorout.py:507: CoverageWarning: Module pydra.tasks.datalad was never imported. (module-not-imported) self.warn(f"Module {pkg} was never imported.", slug="module-not-imported") so I thought I need to add something to dev
3. also, I have this ModuleNotFoundError: No module named 'datalad.api' in the test check too. I added datalad here but it seems not working?

we can either solve it this week or during our hackday next week?
thank you!