Review QtOPCUA examples

There are four OPCUA examples

• OPCUA viewer example
• OPCUA X509 example
• Waterpump
• Quick waterpump

See whether they are worth keeping, if so review each for conformance with current standards outline by https://wiki.qt.io/Qt6/Example-Guideline.

The example docs, the UI and the sources should be checked against compliance with the above guidelines as much as that is possible without OPCUA knowledge.