Add option to enable Pre-Release / Beta updates

[OrangeZXZ]

Is your feature request related to a problem? Please describe.
Currently, pre-releases and beta versions are not downloaded unless they are explicitly enabled per app. I often want to try beta or pre-release versions, but enabling this individually for each app is inconvenient.

Describe the solution you'd like
Add an option that allows enabling pre-release/beta updates.
When this option is enabled for an app, the update checker should also include pre-releases and beta versions and allow them to be downloaded automatically.

Describe alternatives you've considered
A global setting that enables pre-release/beta updates for all apps, instead of configuring this option per app.

Additional context
No additional context needed.

[rainxchzed]

@OrangeZXZ I implemented this feature very recently - #251 - you will be able to use this starting from the next release! (btw you also can choose the version of the app not just release channel!)