Unify project/group hooks codebase

Problem to solve

We have separate controllers for project and group webhooks:

• https://gitlab.com/gitlab-org/gitlab/blob/3c3664ba2a8cc7840453c244f29d27f4bc8dd388/app/controllers/projects/hooks_controller.rb#L72
• https://gitlab.com/gitlab-org/gitlab/-/blob/3c3664ba2a8cc7840453c244f29d27f4bc8dd388/ee/app/controllers/groups/hooks_controller.rb#L76

And separate API controllers:

• https://gitlab.com/gitlab-org/gitlab/blob/3c3664ba2a8cc7840453c244f29d27f4bc8dd388/lib/api/project_hooks.rb#L23
• https://gitlab.com/gitlab-org/gitlab/blob/3c3664ba2a8cc7840453c244f29d27f4bc8dd388/ee/lib/api/group_hooks.rb#L12

But they share the same view, which leads to issues like:

• #238876 (closed)
• #10484 (closed)

When we add some functionality to project level hooks, but forget to add it to group level.

Proposed solution

Unify some parts of parameter lists and specs. This way it would be harder to forget about group level webhooks.

Some downside - it will be harder to contribute FOSS only feature since it will require also contributing to EE.