Add a populate capabilities flag for brand data

[arunshenoy99]

Proposed changes

This PR adds a $populate_capabilities flag to the brand data configuration to ensure it is populated only when needed.

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: I've removed the flag from the functions in favor of a small change directly in the Config::get_site_capability() method. I've also merged the PR #120 into this PR.