Is your feature request related to a problem? Please describe.
It is possible for L1->L2 messages to fail on L2. This may sound bad, but it's totally fine! Why? Well because we can replay L1->L2 messages in our XDomainMessengers! The smart contract side of things has already been implemented! However, the one hiccup--we haven't actually implemented a "watcher" which will replay all enqueued XDomain messages.

Describe the solution you'd like
Implement a xdomain message replayer which we can replay any failed deposits. This replayer should be able to reply deposits which you are watching, but also it should be able to detect all deposits within a block range & replay them. Allowing all deposits to be replayed lets some altruistic party replay all failed deposits that occur during L2 service outages like upgrades.