Add NER tutorial and update documentation configuration

[cthoyt]

This PR updates NER and related documentation:

1. Adds module-level docstring with examples to gilda.ner
2. Adds top-level gilda.annotate function that exposes it more easily (required adding an additional property to the GroundingInstance class)
3. Adds NER example to the README

This PR also updates the documentation configuration:

1. Set language explicitly (required since sphinx 6 I think)
2. Pun below Sphinx 7 (this breaks a lot of builds now)
3. Update intersphinx dictionary since the old format was deprecated

[bgyori]

Nice, thanks!