Related Change-Set: https://gerrit.wikimedia.org/r/#/c/245881/
Investigate how we can implement the needed functionality in the backend.
Questions to consider:
- have an extension for this?
- integrate into core?
Things that need to be considered (incomplete):
- alter API(s)
- change backend code that writes to watchlists
- change code that shows the watchlist items to check for expired items
- adapt job for notification mails
- extra field for expiration date in watchlist table
Result of this investigation should be something that can be turned into an RFC.