chore: add new slack channel for CAPI working group

This adds a new slack channel to be used for a working group focused
on machine pools in cluster api.

Signed-off-by: Richard Case <richard.case@outlook.com>

Author: richardcase

communication/slack-config/channels.yaml

@@ -85,6 +85,7 @@ channels:
   - name: cluster-api-proxmox
   - name: cluster-api-release
   - name: cluster-api-vsphere
+  - name: cluster-api-wg-machinepools
   - name: cn-dev
   - name: cn-events
   - name: cn-users