[requirements] Transition EM branches to Unmaintained

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

So this patch transitions victoria, wallaby, and xena EM branches to
Unmaintained as follows:
- tip of the given branch will be tagged with <series>-eom tag
- unmaintained/<series> branch will be cut from <series>-eom tag
- stable/<series> branch will be deleted

Some further notes:
- stable policy still applies
- backports can be pushed against unmaintained/<series> branch
- openstack-unmaintained-core group 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: Ic47e05836819a01feea815af418448fec192bd0d

deliverables/victoria/requirements.yaml

@@ -11,3 +11,10 @@ branches:
   - name: stable/victoria
     location:
       openstack/requirements: fc679c617443a8f99601c67454842dd51d02b94c
+  - name: unmaintained/victoria
+    location: victoria-eom
+releases:
+  - version: victoria-eom
+    projects:
+      - repo: openstack/requirements
+        hash: a88a0be4666544c304fdb6f77eecc5800fd89b11

deliverables/wallaby/requirements.yaml

@@ -11,3 +11,10 @@ branches:
   - name: stable/wallaby
     location:
       openstack/requirements: 040e24a73f93c5f1c81fc2312a3552f4cb972cc5
+  - name: unmaintained/wallaby
+    location: wallaby-eom
+releases:
+  - version: wallaby-eom
+    projects:
+      - repo: openstack/requirements
+        hash: 015717ea1bcc3aa5060bf2257f8438d7b8655621

deliverables/xena/requirements.yaml

@@ -11,3 +11,10 @@ branches:
   - name: stable/xena
     location:
       openstack/requirements: 51fa0f216cc4a8b391bb68c504127219c115652f
+  - name: unmaintained/xena
+    location: xena-eom
+releases:
+  - version: xena-eom
+    projects:
+      - repo: openstack/requirements
+        hash: 4beb369bc42eed6a2155206588bc0a2860a94ebc