[bug 1191822] Add indexes to heartbeat Answer model
[bug 1191822] Add indexes to heartbeat Answer model

This adds indexes to the heartbeat Answer model to make querying faster
for Gregg.

staranjeet/fjord,lgp171188/fjord,hoosteeno/fjord,lgp171188/fjord,staranjeet/fjord,mozilla/fjord,mozilla/fjord,hoosteeno/fjord,Ritsyy/fjord,mozilla/fjord,Ritsyy/fjord,lgp171188/fjord,lgp171188/fjord,hoosteeno/fjord,Ritsyy/fjord,Ritsyy/fjord,hoosteeno/fjord,staranjeet/fjord,mozilla/fjord,staranjeet/fjord