Adds algorithm to the pages domain key and remote mirror credentials encrypted attributes for forward compatibility with attr_encrypted 3.0.0.

aes-256-cbc is the default algorithm for attr_encrypted 1.x, but the default is changed in 3.0 and thus must be declared explicitly.

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4216/ for more information. This will prevent OpenSSL errors once the code from that MR is merged into EE.

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- Finish user/group/project sections
- Give more .gitlab-ci.yml examples

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