fix(live-update): make fetchLatestBundle method asynchronous

[michaelwolz]

Minimal implementation of asynchronous version of the fetchLatestBundle method which somehow seems to block UI rendering when being called on app startup.

As discussed, this obviously needs to be tested thoroughly. Also the NonEmptyCallack types need to be checked because some path call it with null atm.

Pull request checklist

Please check if your PR fulfills the following requirements:

• [-] The changes have been tested successfully (only checked the fetchLatestBundle for now).
• [ ] A changeset has been created (npm run changeset).
• [ ] I have read and followed the pull request guidelines.