Replace ThreadLocal in Sentry with HubStorage and a wrapped ThreadLoc…

[adinauer]

…al Hub; also fix Webflux integration and add transaction support for webflux

:scroll: Description

Hackweek project 2022

:bulb: Motivation and Context

• Leak less resources on App server redeploy via ThreadLocal (leaked Hub before, now just a few smaller data structures) #2079
• Fix random breadcrumbs during high server load for Webflux #1790
• Add transaction support for Webflux #1807

:green_heart: How did you test it?

:pencil: Checklist

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

:crystal_ball: Next steps

• More testing
• Fix tests
• Cleanup code

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[alphec]

Sorry for commenting on this issue specifically, but there is no clear place where this comment should go.

I wonder what the current state of error reporting and automatic transaction capturing with Spring WebFlux is - especially with the Sentry client 6.5.0. I see a couple of PRs that seem related to these issues. I wonder if there is a plan to move forward and maybe areas where help is needed.

[adinauer]

Closing this in favor of https://github.com/getsentry/sentry-java/issues/2546