Fix site capability transient filter issue

[arunshenoy99]

Proposed changes

1. Moves the filter from the BH plugin's bootstrap.php file to the data module, where other filters are located, and includes the is_callable check. This approach is much safer.
2. Addresses an issue where the current code caused the code in SiteCapabilities.php to be unreachable. As a result, capabilities from the Hiive API were never retrieved, leaving canMigrateSite as the only capability set on any customer site.
3. Updates the code to use the pre_set_transient filter, which is a much safer option in this case (given 2). This filter checks for an empty value only when the transient is being set in the database, ensuring it is set only for sites where the Hiive API has failed.

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

[circlecube]

See https://github.com/bluehost/bluehost-wordpress-plugin/releases/tag/3.14.3 and bluehost/bluehost-wordpress-plugin#1260