[Release Planner]: Add Ad-hoc Release Validation before generating SDK PR or Release Request

We need the Release Planner to perform an ad-hoc validation check to ensure a release is valid before generating an SDK pull request or creating a release request. This step helps prevent invalid releases from entering the pipeline.

Spec Merged in Public Main Repo
- The release must start with a spec that is already merged into the public main repository.

Target Latest Version
- Ensure the release targets the latest preview or GA version as applicable.

Correct Release Type
- Identify whether the release is based on Swagger or TypeSpec, and confirm the type is correctly set.
- I double checked, there are some cases for creating release request for service moving to tsp, but no the other way.