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