Implement compile-time flag to disable automatic update checks.

[libklein]

Description

This PR adds a compile-time flag to disable automatic updates (cf. #4796). Specifically, it prevents the update button from being shown/updated if the Updater detects that an update is necessary. A potential drawback of this approach is that it also does not show the button if the user "requests" this, e.g., by enabling beta updates.

An alternative implementation could also simply disable the automatic update check on application startup.

I believe that the former approach is more desirable as it ensures that the Updater class is in it's expected state regardless of whether updates are disabled or not. We could, for instance, silently log that the application is out of state.

[Mm2PL]

Chatterino never updates automatically without the user's explicit action. It only checks for updates and displays a prompt (which I believe to be an important enough distinction to mention).
Please don't just hide the button. This approach results in wasted requests to the update server. Instead please look at src/singletons/Updates (notably Updates::checkForUpdates) and disable updates there.
Disabling updates at compile time IMO should never have the app call home, it's something I'd consider an antifeature.

[pajlada]

• what mm2pl mentioned, I think I prefer the network request not being run in the first place

[libklein]

Sounds good!

I'd personally prefer disabling the updates by removing the call in https://github.com/Chatterino/chatterino2/blob/master/src/RunGui.cpp#L273 instead of modifying Updater.cpp directly. This way the class itself remains functional, it'll just not be triggered.

I'd also suggest disabling https://github.com/Chatterino/chatterino2/blob/master/src/Application.cpp#L190 to stay consistent - otherwise we'd have to trigger an update check on startup based on the betaUpdates setting. I actually think that hiding the beta checkbox/ignoring the setting altogether is probably in line with the PR, given that it's motiviation is to stop annoying users that source chatterino from a package repository with update notifications. I do see that this is debatable tough.

Happy to hear your opinion on this!

[pajlada]

Instead of ifdefing out the calls to checkForUpdates, I'd rather have this check just early return in the checkForUpdates itself

[Mm2PL]

lgtm

[pajlada]

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