DOC: Fix cross-referencing to API methods and functions

[VeckoTheGecko]

Unfortunately, I am only able to refer to classes, and not their methods, i.e. the following doesn’t create the link to the method:

I dug a bit deeper into this, I also couldn't get it to link to methods either with the current setup - though I think that's due to our current config.

I tested the following

## works
{py:obj}`parcels.ParticleSet` 
{py:class}`parcels.ParticleSet`

## broken
{py:meth}`parcels.ParticleSet.execute` 
{py:meth}`parcels._core.particleset.ParticleSet.execute` 
{py:obj}`download_example_dataset`

On the https://myst-parser.readthedocs.io/en/latest/syntax/code_and_apis.html#sphinx-autodoc2 page it has the following example

- {py:obj}`myst_parser.sphinx_ext.main.setup_sphinx`
- [](#myst_parser.sphinx_ext.main.setup_sphinx)

which properly links to a function. I think the solution might be in the fact that they're using autodoc2 instead of autodoc (maybe the way that generates references is different to what we have).

Should I make this into a separate issue to be pursued later @erikvansebille ? I think cross linking with the classes is suitable for now/a bit lower on the chopping block

Originally posted by @VeckoTheGecko in #2442 (comment)

[VeckoTheGecko]

I found that the problem lies in misconfigured templates in docs/_autoapi_templates introduced in a5d7a64 (#2395) . The only visual difference between the two I can see is the sectioning in the left sidebar.

Investigating more...

[VeckoTheGecko]

I think the differences between the two versions of API reference are quite minor - I'm going to go ahead and remove the templates and put up a PR

EDIT: Actually, maybe its best we chat about this @erikvansebille since you might be more up to date with this

[VeckoTheGecko]

Fixed in #2464