Ability to cancel updates and disable automatic updates

[DGCK81LNN]

Also on auto-updates (related to metered connections): You can't cancel them. There is a cancel button which doesn't work. Neither right click. Seemingly the only option is to rapidly quit lazer (not tested, and it's pressing Command-Q or Alt-F4, 2 or 3 times. Also not sure if this should be a separate issue).

Originally posted by @JacksonChen666 in #30031 (comment)

Sometimes lazer updates break custom rulesets and memory readers and stuff and I may prefer to temporarily stay on the previous version. The problem is that I can't stop the game from updating itself. The 'x' button in the notification doesn't seem to do anything. The only obvious way to stop the update is to quit the game.

(Searching about canceling updates in the repo and I found this commit from 2021 which says Disable cancelling of update via notification; not sure if this is relevant, but the file that was changed in this commit no longer exists now.)

It would be nice to allow opting out of automatically downloading updates. Stable automatically updates because it is stable. Lazer is not stable, it's arguable people may want to temporarily stay on an older version if the latest one isn't working perfectly. In this case, perhaps we can still check for updates but show a confirmation before actually downloading.

The client could have been a bit smarter and stop automatically checking for updates when it can tell I have manually downgraded to an older version. Perhaps store the version number of the latest release that the user has ever used.

[sineplusx]

You can turn off automatic updates completely using the environment variable OSU_EXTERNAL_UPDATE_PROVIDER=1.
This is intended for distribution scenarios where a package manager controls the updates of software (mostly Linux), but can be used in that way too.