add Slack channel for the vcluster project

Author: Rich Burroughs

communication/slack-config/channels.yaml

@@ -438,6 +438,7 @@ channels:
     id: C0ELB338T
   - name: ug-vmware
   - name: undistro
+  - name: vcluster
   - name: velero-dev
   - name: velero-users
     id: C6VCGP4MT