BUG DOC: module docs in solarsystem is broken for some modules

solarsystem is just an alias namespace for a couple of modules, e.g `imcee`, but unfortunately navigating to the module from the solarsystem module is broken, and instead we rendered there an empty docs page.

E.g. https://astroquery.readthedocs.io/en/latest/solarsystem/imcce/imcce.html which should instead point back to https://astroquery.readthedocs.io/en/latest/imcce/imcce.html

Start with the documentation generation or navigation entry point responsible for the solarsystem alias, then compare the broken solarsystem/imcce/imcce.html URL with the canonical imcce/imcce.html page. Done means navigating through solarsystem to an aliased module reaches the canonical documentation instead of an empty page.

Written by the indexing model from the issue text.