Add Let's Encrypt application settings
What does this MR do?
EE counterpart of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27361/diffs#2cda0c6171fa7d04989507a1dd112e34c40df46d
EE counterpart of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27361/diffs#2cda0c6171fa7d04989507a1dd112e34c40df46d