API: Decide on keyword only API

[VeckoTheGecko]

Description

I was looking through the tutorial to see how we're using our functions, and to decide on which API should be keyword only. These are my thoughts

• parcels.FieldSet.from_sgrid_conventions
  • make mesh, vector_fields, skip_field_data_validation keyword only
• parcels.FieldSet.from_ugrid_conventions
  • make mesh, vector_fields keyword only
• parcels.ParticleSet.__init__
  • make particle initial values keyword only
• ParticleFile.__init__
  • leave as is (minimal chance of confusion)
• the rest - keep as is

This is a bit subjective. Happy to discuss if you have other thoughts @erikvansebille

Checklist

• Closes Enforcing keyword-only arguments in certain API #2716
• Tests added
• This PR targets the correct branch (main for normal development, v3-support for v3 support)

AI Disclosure

None used

[VeckoTheGecko]

(I still need to update the test suite and the docs, but that is quite straightforward)

EDIT: Done

[erikvansebille]

Yep I agree with this list. PR looks good