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

`allow_local_requests_for_hooks_and_services` was renamed to
`allow_local_requests_for_web_hooks_and_services`.

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.

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

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

Previously, we used brackets to denote the tier badges,
but this made Kramdown, the docs site Markdown renderer,
show many warnings when building the site. This is now
fixed by using parentheses instead of square brackets.

This was caused by [PREMIUM] looking like a link to
Kramdown, which couldn't find a URL there.

See:
- https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/484
- https://gitlab.com/gitlab-org/gitlab-ce/issues/63800

Many small fixes to api docs which were merged from EE to CE,
and tables cleaned up, as noted in issue
https://gitlab.com/gitlab-org/gitlab-ce/issues/64072

Squashing a few commits and continuing work
on merging the 12 api docs that have not
been ported to CE yet.

Changes migration and all other places the attribute is used