Update release notes for 1.14

Pinging @larkost and really everyone else. This is almost entirely from the closed tickets on the 1.14 milestone excluding bugs that seemed like they never made it into releases, but there are likely things missed and/or things that should be excluded. I tried to mention the bits of backward incompatibility in the "Compatibility" block.
This is incorrect. We show an issue in the web UI to notify users of an out of date index, and point them to the docs to fix it via a command.

> Added a notification and helpful message for out-of-date secondary indexes