update DaWGs meeting to one hour later UTC for Winter

[samccann]

Push to 16:00 UTC so that the time remains at 11AM ET once daylight savings ends. See #579 (comment).

Also need to edit https://github.com/ansible/community/wiki/Docs to say 16:00 UTC.
And change matrix reminder bot to move the DING DING DING reminder out to 15:00 UTC (on hour before the meeting), and the room cyb-clock-clone meeting reminders every 15 minutes during the meeting.

[samccann]

Steps to update the matrix roombot:

• !listreminders - to see what we have set
• !cancelreminder DING DING DING! DaWGs (documentation working group meeting) happening in 1 hour
• !remindroom every 1w; tuesday at 15:00; DING DING DING! DaWGs (documentation working group meeting) happening in 1 hour
• !cancelreminder cyb-clock chimes - 15 minutes have past
• !remindme cron 15,30,45 16 * * tue; cyb-clock chimes - 15 minutes have past
  see https://github.com/anoadragon453/matrix-reminder-bot/#usage for full details

(note the 16 above is 16:00 UTC, the Winter UTC time.