We call `Project#mark_stuck_remote_mirrors_as_failed!` from the
`Git::BaseHooksService`. So that gets called every time we push tags
or branches.

Before this would only mark started mirrors as failed if they had
been started 24 hours ago. A push would never take 24 hours,
especially not when we run it so often.

Lowering that threshold 1 hour should at least allow us to retry
broken mirrors more often on pushes.

The timeout for the initial push is set somewhat longer to accommodate
for pushing large repos. Both numbers are currently picked arbitrarily.

Show disabled mirrors with a badge so that they
can be deleted by project owners.

Prepares us for upgrade to Rails 5.2

Model.new.attributes now also returns encrypted attributes.

Renamed UrlValidator to AddressableUrlValidator to avoid 'url:' naming collision with ActiveModel::Validations::UrlValidator in 'validates' statement.
Make use of the options attribute of the parent class ActiveModel::EachValidator.
Add more options: allow_nil, allow_blank, message.
Renamed 'protocols' option to 'schemes' to match the option naming from UrlValidator.

Retries in Sidekiq and in the remote mirror scheduler can cause repeated
attempts in quick succession if the sync fails. Each failure will then
send an e-mail to all project maintainers, which can spam users
unnecessarily.

Modify the logic to send one notification the first time the mirror
fails by setting `error_notification_sent` to `true` and reset the
flag after a successful sync.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56222

[master] SSRF - Scan Internal Ports and GCP/AWS endpoints

See merge request gitlab/gitlabhq!2689

The email is sent to project maintainers containing the last mirror
update error. This will allow maintainers to set alarms and react
accordingly.