Add repo: devstack-plugin-open-cas

Caching software open-cas is needed in volume local cache feature. Repo
devstack-plugin-open-cas is to configure open-cas for devstack.

open-cas: https://open-cas.github.io/
Nova Spec: https://review.opendev.org/#/c/689070/
Cinder Spec: https://review.opendev.org/#/c/684556/

Depends-On: https://review.opendev.org/#/c/711878/
Change-Id: I54b5a420519386f74b525946c6b54d228df86520
Signed-off-by: Liang Fang <liang.a.fang@intel.com>

reference/projects.yaml

@@ -3183,6 +3183,10 @@ Quality Assurance:
       release-management: none
       repos:
         - openstack/devstack-plugin-cookiecutter
+    devstack-plugin-open-cas:
+      release-management: none
+      repos:
+        - openstack/devstack-plugin-open-cas
     devstack-tools:
       repos:
         - openstack/devstack-tools