Adds few utilities for stretched coordinates + Docs/Grids section on how to use these utils

[navidcy]

Originally developed at CliMA/ClimaOcean.jl#565

This PR brings utilities for constructing variably-spaced coordinates from ClimaOcean to Oceananigans. Namely ExponentialCoordinate and ConstantToStretchedCoordinate. The main features implemented in this PR are in src/Grids/coordinate_utils.jl + the Docs/Grids corresponding section that demonstrates their functionality.

The PR also makes minor several fixes in other docstrings.

Docs preview at https://clima.github.io/OceananigansDocumentation/previews/PR4623/grids/#Coordinate-helper-utilities

[glwagner]

I suggest we merge this and leave the StretchedCoordinate to be vertical-coordinate specific in ClimaOcean?

What's the rationale? I think there are disadvantages to overlapping scope between the packages so it'd nice to clarify what-belongs-where. I think ClimaOcean concerns should be focused on OceanSeaIceModel whereas anything to do with grid generation is more fundamental and seems to be an Oceananigans concern?

[glwagner]

we could relax the Function constraint in this PR as well

[navidcy]

We need to have a unique type otherwise it's not picked up by validate_dimension_specification method.
I defined a new abstract type.

[navidcy]

I agree with the comments. I'll make the changes and ping you!

[navidcy]

I suggest we merge this and leave the StretchedCoordinate to be vertical-coordinate specific in ClimaOcean?

What's the rationale? I think there are disadvantages to overlapping scope between the packages so it'd nice to clarify what-belongs-where. I think ClimaOcean concerns should be focused on OceanSeaIceModel whereas anything to do with grid generation is more fundamental and seems to be an Oceananigans concern?

Yes, feels natural.

[navidcy]

@glwagner, I brought everything here and renamed it to coordinate_utils.jl. Have another look. When merged, I'll delete from ClimaOcean.