Add splunk service
Add splunk service

This will allow shipping app and router logs to splunk[1]

This will is only bound on the API because we're only interested in
paas router logs for the time being

1: https://github.com/alphagov/paas-csls-splunk-broker/blob/main/docs/user-guide.md

alphagov/notifications-api,alphagov/notifications-api