Add GitHub actions release workflow

[intgr]

Heavily based on the setup in django-stubs:

• https://github.com/typeddjango/django-stubs/pull/1950

Benefits:

• Any maintainer can make djangorestframework-stubs releases, not just me and sobolevn.
• Hopefully this will result in more frequent releases (can avoid issues like #652).
• One fewer manual step, one less thing that can go wrong. In particular, this will prevent gaffes like #362.
• Maintainers can't inject malicious code into the PyPI release that doesn't exist in git (though we now have to trust GitHub to be not malicious).

[intgr]

@sobolevn needs to configure a PyPI trusted publisher, I'm guessing this should be:

Owner: typeddjango Repository name: djangorestframework-stubs Workflow name: release.yml Environment name: release

(Related discussion in django-stubs: https://github.com/typeddjango/django-stubs/issues/2114)

[intgr]

Pinging @flaeppe as the author of original django-stubs release workflow.

[sobolevn]

Working on it!

[sobolevn]

Done!

[intgr]

Now all we need is an excuse to make another release to test it 😁