Harmonize CES registry keys

[ppxl]

There are some CES registry keys that do not adhere to the standardized registry naming scheme (that is: snake_case). Please harmonize the existing registry keys to the naming scheme:

• nexus.repository.sandbox.enable
• installDefaultDockerRegistry
• disableOutreachManagement

I suggest these new keys:

• enable_repository_sandbox
• install_default_docker_registry
• disable_outreach_management

The migration phase is going to take a while, presumely 1 year. During this phase both old keys and new keys are supported. Conflicts are resolved by copying the old key (if existent) to the new key. Then the old key is going to be deleted, with the new key being actively used.

After one year and rising log warnings, the support for old keys should be dropped. A separate issue should be opened for dropping the support.

[ppxl]

There is so much space for errors, migration of registry keys should actually be highly testable. I suggest it to be a https://github.com/cloudogu/doguctl feature.