CI: Reorganise .zuul.yaml into multiple files

This allows us to add new jobs and relevant configs in an organised
manner

Change-Id: I2be062d3f634994dc7ffe98b6471df59b0777e1e
Signed-off-by: Michal Nasiadka <mnasiadka@gmail.com>

zuul.d/project-templates.yaml

@@ -73,10 +73,3 @@
       jobs:
         - publish-openstack-python-branch-tarball
 
-- project:
-    queue: magnum
-    templates:
-      - openstack-cover-jobs-magnum
-      - openstack-python3-jobs-magnum
-      - release-notes-jobs-python3
-      - publish-openstack-docs-pti

zuul.d/project.yaml

@@ -0,0 +1,8 @@
+---
+- project:
+    queue: magnum
+    templates:
+      - openstack-cover-jobs-magnum
+      - openstack-python3-jobs-magnum
+      - release-notes-jobs-python3
+      - publish-openstack-docs-pti