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

Removed the unnecessary line. It would be covered anyway by line 352...

See merge request gitlab-org/gitlab-ce!28228

Add correlation id to all sentry errors

Closes #61699

See merge request gitlab-org/gitlab-ce!28253

delete feature flag when disabling Rugged

See merge request gitlab-org/gitlab-ce!28289

Before this, we were only adding the correlation id to the "acceptable
exceptions" which we handle in code.

But we need to add it to the default raven context so the information
would be available for uncaught exceptions.

Adds suffix to enum methods and changes `in_groups` to
`of_groups`

Many customers forget to include the gitlab-secrets.json file. This adds
a warning that both gitlab-secrets.json and gitlab.rb are not included
in the backup.

This will avoid timestamp comparison issues later within equality check
with attributes