Make FATE age off memory efficient #4130
Description
There is a FATE storage layer named AgeOffStore that cleans up finished fate transactions where the client never inquired about its status. This can happen in the case where the client submits a fate operation and the client process dies.
The way AgeOffStore is implemented it keeps all of the FATE ids in memory. As we use FATE for per tablet operations, it may not be possible to store all of these ids in memory. The age off functionality is still needed, but its implementation needs to be changed to not store everything in memory. A new implementation probably needs to persist data with each fate operation.
May want to defer work on this until #3964 and #4129 are complete.