Exercise the monitoring code in the test suite

Description

Currently we don't do any checking of the monitoring code in the test suite. Full testing of the monitoring/metrics system will require more complex tests than will be comfortable to write in our existing unit/functional test suite, but this MR adds a basic smoke test of the simplest metric we provide (bots-count).

Testing the more complex metrics will require orchestrating or mocking the handling of multiple full Execute requests with concurrently connected peers. We can do this in a further MR in the future to add some more complex testing like this.

Part of #136 (closed)