[Package Manager] updating when using beta packages

[SychO9]

Current Behavior

Production instances have stable minimum stability by default. Sometimes we need to be able to try beta packages, but the update command fails because minimum stability is stable.

Steps to Reproduce

1. Install a beta package (packamanager itself is beta)
2. Run a global update

Expected Behavior

We should be able to update without a hitch.

Screenshots

No response

Environment

• Flarum version: x.y.z
• Website URL: http://example.com
• Webserver: [e.g. apache, nginx]
• Hosting environment: [e.g. shared, vps]
• PHP version: x.y.z
• Browser: [e.g. chrome 67, safari 11]

Output of php flarum info

Output of "php flarum info", run this in terminal in your Flarum directory.

Possible Solution

Perhaps allow changing the minimum stability to beta from the UI, while using --prefer-stable in update commands.

Additional Context

No response

[askvortsov1]

Perhaps allow changing the minimum stability to beta from the UI, while using --prefer-stable in update commands.

Feels like this should be simple enough to do with a setting and a toggle switch