Changes these to use unobtrusive JS

This introduces several changes, but these are all just ported from the
EE project.

Creating new records has been disabled, and all
existing records been migrated to clusters as of
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28534

In the admin user edit form, access level radio button labels didn't have
the correct 'for' value. Clicking on the label did not select the radio
button. This makes usability a bit nicer since the click area is increased
when the label is clickable.

This MR adds new application setting to network section
`allow_local_requests_from_system_hooks`. Prior to this change
system hooks were allowed to do local network requests by default
and we are adding an ability for admins to control it.

- The most common use case for qualified_domain_validator currently is
to allow blank ([]) but not allow nil. Modify the
qualified_domain_validator to support this use case.

Creates a new item in help dropdown to show configured support page link

* Limits raw requests to 300 per minute and per raw path.
* Add a new attribute to ApplicationSettings so user can change this
value on their instance.
* Uses Gitlab::ActionRateLimiter to limit the raw requests.
* Add a new method into ActionRateLimiter to log the event into auth.log

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/48717