WIP: SentryTracingWebFilter

[koenpunt]

📜 Description

Initial attempt to implement #1807

I havent been able to compile the project in IntelliJ IDEA, because I get an error on gradle sync, so the changes here are backported from a consuming application.

💡 Motivation and Context

💚 How did you test it?

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the docs if needed
• No breaking changes

🔮 Next steps

[adinauer]

Thanks @koenpunt for the PR. We have recently released 6.16.0 of the Java SDK which adds support for WebFlux Performance (#2597). Closing this now.