Add update-python-version command to automate Python version updates (#21694)

* New upgrade python to ddev and rename meta script

* Lint

* Add changelog

* Add tests

* Constants refactor

* Rename 21695.added to 21694.added

* Small refactor and ddev test --fmt

* Rename test file and add use fake_repo in tests

* Remove requests and address validate_sha256 comments

* Update constants last and make content variables more descriptive 0097bc6

Author: github-merge-queue[bot]