Add Lagos meetup channel

Meetup group - Lagos, Nigeria

https://www.meetup.com/cloud-native-computing-lagos

@rekcah78 @etiennecoutaud @rbenzair

communication/slack-config/channels.yaml

@@ -352,6 +352,7 @@ channels:
   - name: meetup-guatemala
   - name: meetup-hannover
   - name: meetup-hongkong
+  - name: meetup-lagos
   - name: meetup-lasvegas
   - name: meetup-losangeles
   - name: meetup-manchester