Add paths to deploy key, ensure return controller

What does this MR do and why?

Add paths to deploy key, ensure return controller

For the frontend, add a number of paths that are required on the frontend. These are edit, enable and disable.

Also, rails seems to return nothing instead of an empty list when there are no deploy keys. The easiest way to fix this is to wrap the return within a map.

Let's also add frontend fixtures for the new controller endpoints.

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For #407604 (closed)