[magnum] Transition Yoga to Unmaintained

With the new TC resolution the community replaces Extended Maintenance
with Unmaintained status [1].

So this patch transitions stable/yoga branch to Unmaintained as follows:
- tip of the stable/yoga branch is tagged with yoga-eom tag
- unmaintained/yoga branch will be cut from yoga-eom tag
- stable/yoga branch will be deleted

Some further notes:
- there will no longer be official releases off of yoga branch
- backports can be pushed against unmaintained/yoga branch
- openstack-unmaintained-core and <project>-unmaintained-core groups
  will have the rights to merge patches

For further details please read the resolution [1] & review and +1 this
patch if this is correct as soon as possible.

[1] https://governance.openstack.org/tc/resolutions/20230724-unmaintained-branches.html

Change-Id: I2224695c235c2030c45bbe8ca05e301b9665e63d

deliverables/yoga/magnum-ui.yaml

@@ -15,7 +15,13 @@ releases:
       - repo: openstack/magnum-ui
         hash: 731488eaef5d5b28934af1c77b8e7289759be370
     diff-start: 9.0.0
+  - version: yoga-eom
+    projects:
+      - repo: openstack/magnum-ui
+        hash: ea8a0d3a610b37d9d6bdcb08058d5ceeec722cab
 branches:
   - name: stable/yoga
     location: 10.0.0.0rc1
+  - name: unmaintained/yoga
+    location: yoga-eom
 release-notes: https://docs.openstack.org/releasenotes/magnum-ui/yoga.html

deliverables/yoga/magnum.yaml

@@ -31,7 +31,13 @@ releases:
     projects:
       - repo: openstack/magnum
         hash: 312aa6a86ac8e62f6ed4f1e9473fdabbbb7a4b1e
+  - version: yoga-eom
+    projects:
+      - repo: openstack/magnum
+        hash: 312aa6a86ac8e62f6ed4f1e9473fdabbbb7a4b1e
 branches:
   - name: stable/yoga
     location: 14.0.0.0rc1
+  - name: unmaintained/yoga
+    location: yoga-eom
 release-notes: https://docs.openstack.org/releasenotes/magnum/yoga.html

deliverables/yoga/python-magnumclient.yaml

@@ -11,6 +11,12 @@ releases:
     projects:
       - repo: openstack/python-magnumclient
         hash: 1f5edf419d5c64cd428661d3ac666488f9e4a6a6
+  - version: yoga-eom
+    projects:
+      - repo: openstack/python-magnumclient
+        hash: d8158debd084d7d3d362fb865acee31a7fa9a7bc
 branches:
   - name: stable/yoga
     location: 3.6.0
+  - name: unmaintained/yoga
+    location: yoga-eom