resource scheduler: agent instrumentation

[sanderr]

Implement the interaction between scheduler and agent. Make sure the scheduler can drive the agent on a per-resource basis. Make sure the old mode still works when the config option (part of #8009) is set.

• start scheduler on the agent if the new mode is selected

• implement Scheduler._run_task to request an executor and to delegate the resource action request to it, focus on deploy only

• add test with dummy executor

• clean up

  • collect discussion points in slides?

• merge PR 1

• look into state representation and propagation

• test DB state Vs scheduler state

• process failures appropriately

#7561 already contains parts of this, though it was created before the resource scheduler design, it may or may not be easier to just start from scratch