[maintenance] Have a GH CLI extension as an entry point for release automation

[webknjaz]

What's the problem this feature will solve?

I noticed that some of the release automation activities involve running bare GH CLI commands with arguments that have to match pre-release activities. This might be error-prone. Instead, the process could benefit from having simpler commands that mostly just point to things like a PR number.

Describe the solution you'd like

Have a GH CLI extension so that it's possible to use it as an entry point instead of more complex subcommands. A-la gh pytest-infra release --version=9.0.1.

Additional context

https://docs.github.com/en/github-cli/github-cli/creating-github-cli-extensions#tips-for-writing-interpreted-github-cli-extensions