Internal release - Automation to fetch applicable versions

Context

To remediate GiLab Dedicated instances within remediation SLAs, release managers need to build and deliver a private package to such instances. GitLab Dedicated runs the patch set version N-1 out of the three supported minor versions (N, N-1, and N-2) but the actual version will depend on the release schedule and the weekly maintenance.

To accommodate for all the scenarios, the investigation #20621 (closed) concluded private packages should be prepared for N-1, and N-2 versions #20621 (closed):

Decision 🏁

Considering N, N-1 and N-2 are the three minor versions within our maintenance policy, Internal release is done for N-1 and N-2.

Example: On time date 2024-10-28, 17.6 is the active version, the three minor versions within our maintenance policy are 17.5, 17.4 and 17.3. Thus, in case internal release is needed today, they would be done for 17.4 (N-1) and 17.3 (N-2).

Proposal: Add a service to fetch the applicable versions for internal releases

A service should be implemented to retrieve the versions required for internal releases. For example if 17.5, 17.4 and 17.3 are the supported versions within the maintenance policy, the service should return 17.4 and 17.3.