Part of adding Let's Encrypt certificates for pages domains

Add acme-client gem

Client is being initialized by private key stored in secrets.yml
Let's Encrypt account is being created lazily.
If it's already created, Acme::Client just gets account_kid by
calling new_account method

Make Let's Encrypt client an instance
Wrap order and challenge classes

Try to simplify feature flag checks by using policies

There are two cluster hierarchies one for the deployment platform and
one for controllers. The main difference is that deployment platforms do
not check user permissions and only return the first match.

Instance level clusters were already mostly supported, this change adds
admin area controllers for cluster CRUD

Store Let's Encrypt account email in application settings
Also add explicit terms of service consent

Forbid the usage of reload

Closes #60218

See merge request gitlab-org/gitlab-ce!27125

The `#reload` makes to load all objects into memory,
and the main purpose of `#reload` is to drop the association cache.

The `#reset` seems to solve exactly that case.

Add columns to store project creation settings

Add project creation level column in groups
 and default project creation column in application settings

Remove obsolete line from schema

Update migration with project_creation_level column existence check

Rename migrations to avoid conflicts

Update migration methods

Update migration method