Enable application service registration files to be fully editable

Currently they aren't, and you can only set a very thin subset of fields. This isn't good enough for most tests, particularly IRC bridge integration tests, which need experimental flags.

Start by locating the application service registration handling and the IRC bridge integration tests mentioned in the issue. Check which registration fields are currently supported and how experimental flags are represented. Done means registration files can edit the full relevant field set and the IRC bridge integration tests can express their required experimental flags.

Written by the indexing model from the issue text.