text: Title: Automate stable release workflow
  Body: **Description of the issue**
  The release process for stable cirq verions is currently a manual process documented in https://github.com/quantumlib/Cirq/blob/67090465ba60a1ba1fdb8926defa3a465d52cc22/release.md. This documentation is out of date because of changes to the underlying tools.
  
  The release process doesn't have to be manual. we already automate the prelease process which packages and uploads cirq to pypi after each PR merge https://github.com/quantumlib/Cirq/blob/main/.github/workflows/release-main.yml.
  
  A similar workflow should be created that gets triggered by a github realease ... that's the process for creating a stable release shoudl be just a two step operation: 1. update the cirq version 2. create a github release (Which triggers the realease workflow) which is what we do for other quantumlib libraries like [QSim](https://github.com/quantumlib/qsim) https://github.com/quantumlib/qsim/blob/master/.github/workflows/release_wheels.yml