Fix unnecessary capability calls

[arunshenoy99]

Proposed changes

1. This PR introduces a new $populate_capabilities flag when retrieving brand data.
2. Moves REST API initialization to admin (RestApiFilter was also retrieving capabilities for a commerce check, which was unnecessary).

Goes with: newfold-labs/wp-module-onboarding-data#121

This was the shortest way I could find to update the functions without breaking all the other code that uses this.

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Video

Checklist

• I have read the CONTRIBUTING doc
• I have viewed my change in a web-browser
• Linting and tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[wpscholar]

Update: We've removed the flags from the functions in favor of a small change in the Config::get_site_capability() function.