Write specs for as many pre-existing Consensus-related SDET tests as we can

This is a follow-up to https://github.com/input-output-hk/ouroboros-consensus/issues/577, which merely establishes the document with a few specs that we’ve discussed recently (and prompted this idea).

This task is to review the existing SDET test suite, identify which of those existing tests are relying on Consensus requirements, and explicitly write those down.

# Acceptance criteria
We’ve at least made significant progress towards documenting the Consensus Team’s perspective on the features that SDET is already testing.