Improve generated request specs when no controller actions are added

[klyonrad]

Is your feature request related to a problem? Please describe.

When controller generator is used it generates a requests_spec file that is quite empty. It consists only of the describe .. do .. end block without any helping indication that the user can use stuff like expect(response).to have_http_status(200) like it happens when the simpler RequestSpecGenerator is used.

Describe the solution you'd like

when generating a controller the request spec generated will have a different file name and when it is generated without any action it will add just one spec for an index action with a message about adding a real spec.

Describe alternatives you've considered

TBD

Additional context

This issue is extracted from a wish in #2356

I had the idea that we can move the original PR along by separating the issues.

[JonRowe]

This should be fairly easy for someone to add, but I don't have the time to work on the generators myself.

[klyonrad]

This was fixed with #2399