add API reference links

[reint-fischer]

This PR adds API reference links throughout the documentation, which resolves a TODO note.

Since we use sphinx autoapi (#2395) to build the API reference, and MyST to parse markdown (#1342), we should use the {py:obj} role to refer to parcels objects (see executablebooks/discussions/q-a#1169)

e.g.:

{py:obj}`parcels.FieldSet`

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:

{py:meth}`parcels.ParticleSet.execute()`

See also: https://www.sphinx-doc.org/en/master/usage/domains/python.html#role-py-meth

Notebooks to add links

• quickstart tutorial
• output tutorial
• conceptual workflow
• curvilinear grids
• spherical grids and unit conversion
• delayed starts
• kernel loop
• sampling a field
• StatusCodes
• gsw density
• Argo float
• Diffusion
• Particle-particle interaction
• Interpolator API
• parcels.interpolators (done in fix formatting in dt guide and interpolators guide #2441 )
• timestep and integration method