op-interop-mon: add e2e tests (devstack)

[geoknee]

Context:

I had originally started out integrating this component deeply into the devstack (so that it would be available in every interop acceptance test). However, that turned out to require a lot of boilerplate, and (worse) we had no direct handle on the metrics so needed to expose those over RPC somehow which is very unergonomic.

Here I am taking a more pragmatic approach where the interop-mon is spun up in memory in the test context (outside of the stack itself) and attached to the RPC endpoints of the various chains. NB: I had to fiddle with things more than I liked to expose these RPC endpoints. This approach makes it easy to assert on the monitor's metrics.

Update: in the end exposing raw endpoints was falling foul of some of the cleverness used when pointing tests at kurtosis. So the solution was to allow op-interop-mon to be started with clients instead of rpc endpoints.

This first test is very simple and can be further deepened to assert on more precise things about the metrics.

Towards https://github.com/ethereum-optimism/optimism/issues/16227