Require all templates to use default stages
What does this MR do?
Improves our templates and ensures that all of them are includable and do define a default set of stages if overwritten.
Resolves https://gitlab.com/gitlab-org/gitlab-ce/issues/59992
EE: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10579
Does this MR meet the acceptance criteria?
Conformity
Edited by Kamil Trzciński (Back 2025-01-01)