It consists of two parts:

1. Redirecting users to the configured external storage
1. Allowing the external storage to request the static object(s)
   on behalf of the user by means of specific tokens

Part of https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6829

remove EE specific code
remove EE licence checks
move migration from EE to CE folder structure
move specs from EE to CE folder structure
remove EE specific flag specs

`label_name` is now not excluded by default

Also removed `label: true` from calls to the helper

This whitelists all existing offenses for the various CodeReuse cops, of
which most are triggered by the CodeReuse/ActiveRecord cop.

Partially addresses #47424.

When listing issues and merge requests on dasboard page,
make sure that at least one filter is enabled.

User's id is used in search autocomplete widget instead
of username, which allows presetting user in filter dropdowns.

Related to #43246

When the database is in a read-only state, display a banner on each
page informing the user they cannot write to that GitLab instance.

Closes gitlab-org/gitlab-ce#43937.

Twitter redirects `www.twitter.com` to `twitter.com`

Also removes unnecessary regex escapes, just 'cause.