Bridge: Persist monitor even pulling state.

[musitdev]

Is your feature request related to a problem? Please describe.
Currently, only the Movement monitor persists its state so that when it restarts, the even pull restart is of the same height as when it shuts down.
The Eth monitor doesn't persist its state, so when the Relayer is stopped and then restarted, all events generated during this shutdown time are lost.
The current MVT implementation is highly linked to the monitor.

Describe the solution you'd like
Implement a new version of the persisting algorithm that both chains can use.
The logic is the same for all chains.