Spike: Investigate the possible options to implement HTTP2 support

There are at least two options how to implement HTTP2 server support in the qthttpserver. We already have already an HTTP2 stack in QtNetwork which in parts becomes available via https://bugreports.qt.io/browse/QTBUG-105491 . The current version mostly focuses on the client side of HTTP2.

1. We extend the result of  https://bugreports.qt.io/browse/QTBUG-105491  to cover the HTTP2 server side and then use it in qthttpserver.
2. We don't extend the QtNetwork but implement HTTP2 server side in qthttpserver itself. It should be able to use the new classes to a large extent. We just need to decide internally what to use and work differently based on server use cases.

Definition of Done

• Investigate the above two options and decide on the path forward
• Investigate the gerrit patches from an earlier attempt of achieving this. see gerrit links in https://bugreports.qt.io/browse/QTBUG-95069
• Plan the individual implementation steps such that two developers can work concurrently on this topic. It should cover QtNetwork and QtHttpServer work. The backlog should be attached to https://bugreports.qt.io/browse/QTBUG-95069 as that's the overarching task.