ci/cd: create/use Tailscale users for PyPI and Test PyPI

[dylan-tailscale]

Create a user on both PyPI and Test PyPI for Tailscale that can be used for publishing the Python tailscale-py wheels from the tailscale-rs CI/CD publish workflow.

• User must have 2FA enabled.
• Creds (including 2FA) must be saved in a credential store that only the tailscale-rs owners have access to.
• User must be an owner on the tailscale-py package.
• User must be able to publish new versions of the tailscale-py package to PyPI and Test PyPI via a Trusted Publisher setup.
• User account must be branded with Tailscale logo, etc.
• Individual user accounts (currently Dave, Dylan, and Nathan) are removed from the tailscale-py package; the new Tailscale user is the only owner.

This is a mostly mechanical process; the effort is in testing with our current publishing setup.