[TypeSpec flow] support to deprecate a release plan with business justification

Taking the [release plan #1186](https://aka.ms/sdk-release-planner?release-plan-id=b1e8b8ef-7eb4-ee11-a569-000d3a3411c3) for example. It was originally targeting to release in April. but not yet closed in June. After communication, the service is deprecating and they do not want to proceed any longer.

Start with release plan #1186 and trace the current release-plan closure flow to understand how an active plan is handled after a service is deprecated. Done should include a way to deprecate the plan with a business justification and prevent it from proceeding further.

Written by the indexing model from the issue text.