Debian CRUD group distribution endpoints

Merged Mathieu Parent requested to merge sathieu/gitlab:debian_group_distributions into master

What does this MR do?

To bring group distributions on par with project distributions, this MR adds Debian CRUD group distribution endpoints.

A new feature flag is added too, as proposed by @10io.

Screenshots or Screencasts (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

  • Label as security and @ mention @gitlab-com/gl-security/appsec
  • The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
  • Security reports checked/validated by a reviewer from the AppSec team