[Tracking] Move from Scheduler to Readiness Gates

[thisthat]

Goal

Deprecate the scheduler approach in favor of the Readiness Gates

Details

PoC available in #1701 here #1249 more info available in @RealAnna comment

### Items
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/1445
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/1457
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/1458
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/1459
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/1477
- [ ] https://github.com/keptn/lifecycle-toolkit/issues/1460