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

Signed-off-by: Istvan szalai <istvan.szalai@savoirfairelinux.com>

Introduces new `feature_entry` helper for dashboard.
This helper reduces code duplication when listing available features
and relevant links to configuration sections