Add option to disable tracking megolm session ratchet state

The tracking is meant for bridges/bots that want to delete old ratchet states
after they're not needed, but for normal clients it's just unnecessary overhead

crypto/machine.go

@@ -78,6 +78,7 @@ type OlmMachine struct {
 	RatchetKeysOnDecrypt         bool
 	DeleteFullyUsedKeysOnDecrypt bool
 	DeleteKeysOnDeviceDelete     bool
+	DisableRatchetTracking       bool
 
 	DisableDeviceChangeKeyRotation bool