CI: Use realtime_check_baseline template

The merge_tree variable differs baseline on whether the pipeline runs for a merge request or a baseline. Use a specific template rather than adding the single variable, so we have easier time extending the run if needed in the future.

Bugzilla: INTERNAL Upstream Status: RHEL-only

Signed-off-by: Veronika Kabatova vkabatov@redhat.com