Add an option to check for updates on the selected release channel upon launcher startup

[Peregrine05]

This can help ensure that Chunky users are using the latest release of Chunky, which may decrease the number of issues caused by the use of outdated Chunky versions.

• [ ] Check for updates automatically (recommended)

[leMaik]

This doesn't have an option, but searching for updates is already done by default when opening the launcher.