[TypeSpec flow] Guide and new feature required to enable AutoPR merging for a release.

The discussion is initiated from an AutoPR without a link to release plan. 
[[AutoPR azure-mgmt-web]-generated-from-SDK Generation - Python-5790852 by azure-sdk · Pull Request #44825 · Azure/azure-sdk-for-python](https://github.com/Azure/azure-sdk-for-python/pull/44825/changes/68365990aa96eb09f43245ee5aa8564b0fabda08)

We have agreement that for such PRs, they should be DRAFT as initial state. Even if it is activated by service, it won't be reviewed until the service has a release plan created. 

I was once asked by a service developer, “How can I push changes to the PR produced by MCP?” The response from me was that without a release plan, the PR cannot be merged. This was disappointing, especially for .NET.  More developers use the MCP tool to initiate .NET management plane PRs for further development, while at the end, they are told the PR could not be merged?  However,  if the service creates a release plan afterward, they do not know how to link the AutoPR to it and they must ask for support in the team channel. This situation could be changed if 

- we have clear guide how to push AutoPR produced by MCP.
- release plan supports to link to an existing SDK pull request.