Devops: Release process update

[gmalouf]

With this pull request (and changes already made to the SDK's settings), the release process for the Python SDK will be as follows:

• Run create-release-pr.yml, which creates a release pull request.
• Permissioned user approves the pull request (does not merge themselves)
• Run release.yml, specifying the PR number output from (1) and the release version (tag) as inputs.
• Doublecheck releases page, proper tag created, branch, PR merged/branch deleted, etc.

As a part of this, we moved away from Git Flow to a single mainline branch (named main).

[onetechnical]

Should at least fix the v prefix on version thing. Other comments are good things to modify too.