Require a base job

This makes base jobs required and allows for a per-tenant default.

Story: 2001110
Task: 4793
Change-Id: I26ffddad8358c156cfac749ce98af70f3447f671
diff --git a/tests/fixtures/layouts/rate-limit.yaml b/tests/fixtures/layouts/rate-limit.yaml
index 9392f5e..1f32dbf 100644
--- a/tests/fixtures/layouts/rate-limit.yaml
+++ b/tests/fixtures/layouts/rate-limit.yaml
@@ -25,6 +25,10 @@
     window-decrease-factor: 2
 
 - job:
+    name: base
+    parent: null
+
+- job:
     name: project-merge
 
 - job: