Add RC tag support and fix version discovering

What does this MR do?

1. Fixes version discovering in build process (was broken after !276 (merged))
2. Adds support for building and releasing as Bleeding Edge the vX.Y.Z-RC.N tags

Why was this MR needed?

1. Is needed to properly do releases. 2. is needed to release RC packages (according to !176 (merged)).

Are there points in the code the reviewer needs to double check?

The except and only parts of release jobs in .gitlab-ci.yml

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

!176 (merged)

/cc @ayufan @nick.thomas