Redesign the updater

[loewenheim]

As reported in #1759, the updater always asks for elevated permissions on Windows because the check for writeability of the exe doesn't work there. We should rebuild the updater logic to make this sound, for example by using self-replace.

Moreover, I believe the updater should be feature-gated so that package managers like brew and npm (and nix …) can install a version without it, instead of the hacky checks whether sentry-cli was installed via a package manager.

Open question: what do we do about auto-sudo? Integrating it with self-replace would require some rigmarole.

[github-actions[bot]]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀