Add source and issues urls to metadata

So we can find the repo from the charmhub page.

Change-Id: I3cb6574a475f931d83f324cb314f5aa716a3e601

charms/ovn-central-k8s/metadata.yaml

@@ -23,6 +23,8 @@ description: |
   automatically choose a single active instance.
 tags:
 - networking
+source: https://opendev.org/x/charm-ovn-central-k8s
+issues: https://bugs.launchpad.net/charm-ovn-central-k8s
 
 containers:
   ovn-sb-db-server: