Support of additional release planner scenarios

I am creating this epic to track the GitHub issues associated with completion of implementation to support all additional release plan scenarios in the new UI and back-end implementation. I will add links to GitHub issues as they are created.

- [x] APEX extensions - Private Preview, Public Preview, GA (release plans are supported but need to identify in Release Planner App if the release plan is an extension). - https://github.com/Azure/azure-sdk-tools/issues/7913
- [ ] Release Plans that map to Service, not product - https://github.com/Azure/azure-sdk-tools/issues/7314 https://github.com/Azure/azure-sdk-tools/issues/7522
- [ ] Multi-Product Release Plans - https://github.com/Azure/azure-sdk-tools/issues/7314
- [x] non-APEX: TypeSpec and OpenAPI supported but need to identify if the release plan is non-APEX via the Release Planner App - https://github.com/Azure/azure-sdk-tools/issues/6262
- [ ] (In Progress, requirements & design targeted for end of Jan 2025) Existing HLC SDKs - https://github.com/Azure/azure-sdk-tools/issues/8629
- [ ] (In Progress, requirements & design targeted for end of Jan 2025) SDKs that are released by the SDK team on behalf of the Service Partner - https://github.com/Azure/azure-sdk-tools/issues/8629
- [x] Existing OpenAPI DPG + convenience layer
- [x] TypeSpec DPG + convenience layer
etc.
- [ ] Maintenance release: hot fixes for SDKs
- [ ] Maintenance release: regularly SDK updates like monthly or quarterly refreshes
- [ ] Retirement of service or product REST APIs and SDKs
- [ ] Deprecation or retirement of older API and SDK versions - https://github.com/Azure/azure-sdk-tools/issues/5559

Start by reviewing the linked issues for service-level, multi-product, existing HLC, deprecation, and retirement scenarios, then inspect the Release Planner App requirements and design work they reference. Done means the remaining unchecked release-plan scenarios in this epic are implemented and represented in the new UI and back-end implementation.

Written by the indexing model from the issue text.