Minimalistic `tabby` metadata extractor with datalad-metalad

[mih]

TODO essential features:

• [x] needs to set @id for the root document on the dataset
• [x] needs to set @type for the root document on the dataset
• [x] needs to yield other records from /dscollection

Ping: https://github.com/psychoinformatics-de/datalad-tabby/issues/2

• Closes https://github.com/psychoinformatics-de/datalad-tabby/issues/55
• Closes https://github.com/psychoinformatics-de/datalad-tabby/issues/2

[mih]

Thanks for the review!

One note (not really an issue): I have git v2.31 installed, and 4 tests were skipped locally with:

Git configuration redirect via GIT_CONFIG_GLOBAL only supported since Git v2.32

You will find that many (most?) datalad-next based tests will be skipped on your system. Anything that interacts with a user/system config will not run, because Git versions prior 2.32 do not support the isolation approach that the fixtures use. Given that v2.32 was released more than two years ago, I'd suggest upgrading Git to at least v2.32.

[mih]

I will merge this. I won't stay the way it is, but too many decision will take longer than my window for working on this will be. It is tested, it does what it does.