feat(data): add DataStore 'Advanced Workflows' section; add Custom Primary Key docs

[david-mcafee]

NOTE: to view changes locally:

• gh pr checkout 4452
• yarn && yarn dev
• Navigate to Libraries > DataStore > Advanced Workflows

Description of changes: feat(data): add DataStore 'Advanced Workflows' section; add Custom Primary Key docs

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mikepschneider]

Not directly changed in this PR, but I noticed a small typo.

Under the section Observe Model Mutations in Realtime, in the kotlin->callbacks section, on line 3, postChanged -> is missing.