Migrate qubes-manager tools to Qt6

[marmarta]

The problem you're addressing (if any)

Qt5 will stop being supported.

The solution you'd like

Stop using it.

[alimirjamali]

I believe this is a Major issue. Because of two reasons:

1. Free support for Qt5 ended on 26th May 2023. And extended paid support is only till 26th May 2025. During the paid subscription based support period, security fixes might not be available to Fedora project and others.
2. The major essential PR to Qube Manager might conflict with other PRs if it is not reviewed and merged quickly.