Bulk notify users that issues have been moved

[timja]

1. Should give a link to their watchlist providing them a list of JENKINS ids to GitHub issues links
2. Should be a single email per user rather than the 100s that we risk sending some users.

TODO:

• List of all emails from people that watch issues
• Script / process to bulk notify (using mailgun?)
• Blog post to be published after

[timja]

(from gitter):

For the email list I was thinking something similar to @lemeurherve 's avatar script and then storing the emails in a private repo

If there's a domain with a large amount of emails e.g. gmail we may want to ramp up sending so splitting out large domains
but may not be a concern