Standardize tier1 in gating

The tier1 tests were traditionally run by BaseOS CI by various
tasks if the baseos-ci.brew-build.* family, typically implemented
by Beaker jobs.

Every component used to have its own special flavor of the
configuration, both in BaseOS CI (the triggering part) and here in
the component's gating.yaml (results processing).

The each-component-is-a-snowflake approach didn't work very well,
creating discrepancies like RHEL-140879.

At long last, I've unified the BaseOS CI configuration for all my
components:
- drop the Beaker job(s) (which have been declared obsoleted anyway)
- trigger two OpenStack jobs
  - "fast lane" for architectures where we usually get results fast,
    sometimes it's advantageous to take a look ASAP
  - "slow lane" for architectures we typically have to wait
For reference, it's commit d2baef686 in baseos-qe/citool-config.

Now I'm fixing the counterpart in gating.yaml (results processing):
We wait for the "fast lane" and "slow lane" results and they both
must pass.

gating.yaml

@@ -3,5 +3,5 @@ product_versions:
   - rhel-10
 decision_context: osci_compose_gate
 rules:
-  - !PassingTestCaseRule {test_case_name: baseos-ci.brew-build.tier1.functional}
-  - !PassingTestCaseRule {test_case_name: osci.brew-build.tier0.functional}
+  - !PassingTestCaseRule {test_case_name: baseos-ci.brew-build.gate-build-fast-lane.functional}
+  - !PassingTestCaseRule {test_case_name: baseos-ci.brew-build.gate-build-slow-lane.functional}