Add tagfiles to support fetching documentation with xeus-cpp-lite

[anutosh491]

Hi,

We can currently fetch the standard documentation through xeus-cpp-lite. But we can't yet cover any 3rd party lib.

1. Xeus-cling could fetch xtensor documentation (even without xtensor being installed, because the tagfiles were added to xeus-cling themselves. Check here) . This doesn't sound justified.

2. As discussed with Sylvain in the past, we probably shouldn't populate xeus-cpp with the tagfiles for all repos but rather have them be a part of the repo itself. And then when we do a mamba install %xtensor, these end up in the file system and then can be put to use from there.

Something like

[anutosh491]

cc @JohanMabille

Thought of addressing before the pydata paris talk ;)

Any kind of release would be helpful too

[JohanMabille]

I think we should find a way to generate the tag file from the documentation, otherwise it will be hard to keep them sunchronized. Anyway, let's merge this first version so we have a reference file to compare with when working on the generation of the tags.

[JohanMabille]

Can you run pre-commit to fix the linter before I merge it?

[anutosh491]

Addressed thanks for the review @JohanMabille