Enable passing of service name to '/pd oncall' slack bot

The addition of the /pd oncall has been a great. However, I would like to request (or perhaps there is away I’m not aware) for that command to accept the service name as a parameter.

For example: /pd oncall “My Service”

By adding this functionality, I’d be able to create a scheduled message that would post the above message, every so often so we could see who is next on call.

Thank you!