Add Documentation for ApplyTransforms, and Add Resources to Each and PgSelect Docs

[iamameme]

Description

In my usage of Grafast at my workplace for the past few months, I've fallen in love with it. I've also obtained some learnings that I wish I had read in the docs. This is focused mainly around modifying the keys/values returned from a PgSelect. We have been working through the unique case of having to support a legacy GraphQL schema while not wanting that to affect our database design. This meant writing plans to resolve fields that required changing the returned keys and values from the DB a lot.

Hopefully, these changes might help others that run into similar use-cases.

• Add a new docs page for the ApplyTransforms step
• Add a new section in the each step docs with more example usage
• Add a new section in PgSelect to link to each and applyTransforms to describe additional behavior a user may be interested in

Question that prompted this: https://github.com/graphile/crystal/issues/2161

Performance impact

• None

Security impact

• None

Checklist

• None (Doc changes)