Software upgrade w/backpressure test cases

### Background

We should add a test case and investigate at least this one particular scenario:
- Before a software upgrade, have one CN's BN stop sending acknowledgements and have that CN fall into CHECKING due to backpressure.
- Then immediately perform the software upgrade
- 3/4 other nodes restart
- Then allow block acknowledgements back to the first CN
- What happens?

### Acceptance Criteria

Implement the above test case

### Dependencies

_No response_

### Definition of Ready (DoR) Checklist

- [ ] Clear acceptance criteria
- [ ] Clear and detailed description
- [ ] Dependencies identified
- [ ] Links to documentation
- [ ] Should be completable in 2-3 Days
- [ ] Initial draft of Low-level design document
- [ ] At least high level test plan
- [ ] Groomed/Estimated

### Definition of Done (DoD) Checklist

- [ ] Acceptance Criteria complete
- [ ] No Codacy issues greater than minor (in new code)
- [ ] JavaDocs updated/created
- [ ] Code commented
- [ ] Unit tests created/updated
- [ ] 80% test code coverage (in new code)
- [ ] Happy Path and major negative cases in HAPI tests as applicable