Facilitate async debug entries in Site Health Info

[westonruter]

I noticed that loopback request test is not included in the Site Health Info. It seems that no asynchronous tests are included in the debug information with the exception of the hard-coded wp-paths-sizes. In the same way that site_status_tests allows for specific tests to be async, it would be great if debug_information allowed the same. Other existing core tests should be included in the Site Health Info as well, specifically the tests dotorg_communication, background_updates, and loopback_requests.

For some context: I work on the AMP plugin and loopback requests are essential for the plugin to work properly. When users create support forum topics with their Site Health info, it would be very helpful if the result of the Loopback Requests test were included in the debug info.