Cadl Azure Core library release process requirements for Release Planner

### Background:

- In the description of "Approval & release process for Cadl Azure Core library" Epic https://github.com/Azure/cadl-azure/issues/2402 there is mention of the release process for the Cadl Azure Core library "This should also include how teams will be notified, migration strategy, etc.".

- @allenjzhang responded that "for overall spec writers checking into the rest-api-spec repo, it is governed by the onboarding tool process, which I think is this Epic about." I don't think the entire epic is about the release planner but the Release Planner can support the process defined by the Cadl team.

### Questions:

1. How does a team get notified if there is a new version of the Cadl Azure Core library?  
2. What should be communicated to the Cadl users?  Changelog - bug fixes, new functionality 
3. Anything that could potentially impact their existing Cadl docs  
4. What is the migration strategy for moving them from one version to the newest version?  Do the user's need to do anything?  How does this impact existing Cadl docs?  

### Release Planner Requirements

- The Release Planner could notify a user if there is a new version Cadl Azure Core library.  This could be added as a new requirement but this is only part of the Cadl Azure Core library release process.  

- The release planner can drive action items that we want a user to complete.  We need to understand those actions -  Do they need to re-install Cadl?  Do they need to change their existing Cadl docs?