Measure CF-D upgrades appropriately with uptimer

[ctlong]

CF-D pipelines currently use uptimer to capture certain measurements relating to downtime during CF-D upgrades, and to fail them when those measurements exceed certain thresholds. However, due the retry logic we've added to deploys, the thresholds are not being applied appropriately – uptimer may fail a successful deploy, then on a retry the deploy will essentially be a no-op, resulting in no downtime for uptimer to fail on because no change occurred.

### Tasks
- [ ] Reinvestigate and update the thresholds we set on upgrades.
- [x] Remove retry logic from (upgrade?) deploys to ensure that uptimer works well.
- [x] Set reasonable value for `APP_STATS_THRESHOLD` in uptimer config
- [ ] Update uptimer errors post-tear down to improve clarity