Add section for protocol specific information on the admin page (#4910)

This PR adds section for protocol specific information, then always show
both of OStatus and ActivityPub. Specifically, this will help admins to
check PuSH subscription status and unsubscribe manually, even `protocol`
has been changed.

This also includes below changes:

* Add `overflow: hidden` to prevent float leaking
* Add missing fields for ActivityPub