Use `sphinx.ext.autosectionlabel`

[LecrisUT]

I was trying to link to the hierarchy section using intersphinx links, but I couldn't find the target for it similar to how select is available. This is mostly because the sections are not auto-labeled. This should make linking easier for external documentations.

Not sure if autosectionlabel_prefix_document would also be necessary.

Trying to debug using:

$ myst-inv https://fmf--257.org.readthedocs.build/en/257/
fails
$ python -m sphinx.ext.intersphinx https://fmf--257.org.readthedocs.build/en/257/objects.inv
works

Edit: This does resolve my issue, the only question is if autosectionlabel_prefix_document should be used. I don't know what it does when there are label clashes, but to me it seems prudent to add it

std:label
    hierarchy                                Hierarchy                               : features.html#hierarchy

vs

std:label
    features:hierarchy                       Hierarchy                               : features.html#hierarchy