PT43289461: Raise alarms when issues with Mongo

- instruct sec to watch mongodb logs
- added 4 new alarms:
MONGO_FATAL_REPLICATION_STOP raised when a node cannot replicate
MONGO_FAILED_ELECTION raised when there election fails
MONGO_MEMBER_DOWN raised by a node when it cannot see other node in replica set
MONGO_NODE_STATE_CHANGED raised whenever node state is changed