Retire Solum project

Solum project is in inactive list since 2024.1
- https://governance.openstack.org/tc/reference/emerging-technology-and-inactive-projects.html#current-inactive-projects

and there is no leader in 2024.2 cycle.
- https://etherpad.opendev.org/p/2024.2-leaderless

There is no response on last call for maintainers and retirement
notification:
- https://lists.openstack.org/archives/list/openstack-discuss@lists.openstack.org/thread/GD37ISH3TUBH5RQ2CCRZ5YIHE5LHX6G2/

Seeing project inactivities and no maintainers for this project,
this commit propose to retire this project.

Change-Id: If694e20075d8fd93de072a33aeb62fcdcde9c5f7

reference/legacy.yaml

@@ -2117,15 +2117,35 @@ Security:
         - openstack/syntribos-payloads
 
 solum:
+  mission: >
+    To make cloud services easier to consume and integrate with your
+    application development process by automating the source-to-image
+    process, and simplifying app-centric deployment.
   irc-channel: solum
   service: Software Development Lifecycle Automation service
   url: https://wiki.openstack.org/wiki/Solum
-  partial: yes
+  retired-on: 2024-05-10
   deliverables:
     solum-infra-guestagent:
       retired-on: 2016-11-24
       repos:
         - openstack/solum-infra-guestagent
+    python-solumclient:
+      repos:
+        - openstack/python-solumclient
+    solum:
+      repos:
+        - openstack/solum
+    solum-dashboard:
+      repos:
+        - openstack/solum-dashboard
+    solum-specs:
+      release-management: none
+      repos:
+        - openstack/solum-specs
+    solum-tempest-plugin:
+      repos:
+        - openstack/solum-tempest-plugin
 
 swift:
   irc-channel: openstack-swift

reference/projects.yaml

@@ -2483,37 +2483,6 @@ skyline:
     skyline-console:
       repos:
         - openstack/skyline-console
-solum:
-  ptl:
-    name: APPOINTMENT NEEDED
-    irc: No nick supplied
-    email: example@example.org
-  appointed:
-    - zed
-  irc-channel: solum
-  service: Software Development Lifecycle Automation service
-  mission: >
-    To make cloud services easier to consume and integrate with your
-    application development process by automating the source-to-image
-    process, and simplifying app-centric deployment.
-  url: https://wiki.openstack.org/wiki/Solum
-  deliverables:
-    python-solumclient:
-      repos:
-        - openstack/python-solumclient
-    solum:
-      repos:
-        - openstack/solum
-    solum-dashboard:
-      repos:
-        - openstack/solum-dashboard
-    solum-specs:
-      release-management: none
-      repos:
-        - openstack/solum-specs
-    solum-tempest-plugin:
-      repos:
-        - openstack/solum-tempest-plugin
 storlets:
   ptl:
     name: Takashi Kajinami