implement advanced hx-boost overrides

[MichaelWest22]

Description

Try out advanced hx-boost where you can specify swap,target and select as overrides instead of just "true" in the hx-boost attribute value. This lets you have inherited base hx-boost values that redirect all boosted elts to target or select a set element.

Corresponding issue:

Testing

Please explain how you tested this change manually, and, if applicable, what new tests you added. If
you're making a change to just the website, you can omit this section.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded