Non predictable permalinks when multiple automodapi directive is used

[bsipocz]

Identified as an issue in astropy/pyvo#289 (comment)

E.g. here the first one gets the classes and functions link, but the rest just a numbered ID, which is then not very informative to be used elsewhere as a reference, as well as non-future proof, basically making these headings useless to be cross-linked.

Example from the astropy core docs:
docs/modeling/reference_api.rst
https://docs.astropy.org/en/stable/modeling/reference_api.html

One solution could be that the module names are inherited into those heading links, e.g.
https://docs.astropy.org/en/stable/modeling/reference_api.html#functions becomes https://docs.astropy.org/en/stable/modeling/reference_api.html#module-astropy.modeling.functions

While https://docs.astropy.org/en/stable/modeling/reference_api.html#id9 becomes https://docs.astropy.org/en/stable/modeling/reference_api.html#module-astropy.modeling.statistic.functions