[magnum] Transition Zed to Unmaintained

This branch reached the end of its official stable maintained period,
hence this patch transition stable/zed branch to Unmaintained. (For
details about Unmaintained state please see: [1][2])

The transitions is as follows:
- tip of the stable/zed branch is tagged with zed-eom tag
- unmaintained/zed branch will be cut from zed-eom tag
- stable/zed branch will be deleted

Note:
- there will no longer be official releases off of zed branch after this
  transition
- backports can be pushed to unmaintained/yoga branch
- openstack-unmaintained-core (or <project>-unmaintained-core groups if
  such exists) have the rights to merge patches

Important: please +1 if the team is ready for us to proceed with this
transition, or -1 if there are any final Zed stable release with
backports currently in flight that we should wait for. For the latter
case, please propose a final Zed stable release patch, and rebase this
patch on top of that, with the latest commit hash of stable/zed.

The transition deadline is May 2nd, 2024. [3]

[1] https://docs.openstack.org/project-team-guide/stable-branches.html#unmaintained
[2] https://governance.openstack.org/tc/resolutions/20230724-unmaintained-branches.html
[3] https://releases.openstack.org

Change-Id: Iaa3e76f28448dbd4c9bd2bc4696e8c43f8f52abb

deliverables/zed/magnum-ui.yaml

@@ -15,7 +15,13 @@ releases:
       - repo: openstack/magnum-ui
         hash: f8580d7c2b274dec8aed99bb2f83d7c18035ccbb
     diff-start: 10.0.0
+  - version: zed-eom
+    projects:
+      - repo: openstack/magnum-ui
+        hash: cb7a09b0d31297867f3c5513ea0d5474b25f1be5
 branches:
   - name: stable/zed
     location: 11.0.0.0rc1
+  - name: unmaintained/zed
+    location: zed-eom
 release-notes: https://docs.openstack.org/releasenotes/magnum-ui/zed.html

deliverables/zed/magnum.yaml

@@ -27,7 +27,13 @@ releases:
     projects:
       - repo: openstack/magnum
         hash: e79907c521149872c1b495355a3a7b3a0c7e3479
+  - version: zed-eom
+    projects:
+      - repo: openstack/magnum
+        hash: 0ee979099a01ae2c8b1b5d6757897a8993e4e34c
 branches:
   - name: stable/zed
     location: 15.0.0.0rc1
+  - name: unmaintained/zed
+    location: zed-eom
 release-notes: https://docs.openstack.org/releasenotes/magnum/zed.html

deliverables/zed/python-magnumclient.yaml

@@ -15,8 +15,14 @@ releases:
     projects:
       - repo: openstack/python-magnumclient
         hash: 85174f1b44e21bb23d976fa88e167d9eceb29ec1
+  - version: zed-eom
+    projects:
+      - repo: openstack/python-magnumclient
+        hash: faa5d80bcc0843833957509a9e087c1c19778ab9
 branches:
   - name: stable/zed
     location: 4.0.0
+  - name: unmaintained/zed
+    location: zed-eom
 release-notes:
   https://docs.openstack.org/releasenotes/python-magnumclient/zed.html