Add automatic trace support for Spring WebClient

[yhware]

📜 Description

When using WebClient in Spring, automatically add span and breadcrumb for tracing.
There's already support for RestTemplate (https://docs.sentry.io/platforms/java/guides/spring-boot/performance/instrumentation/automatic-instrumentation/)

💡 Motivation and Context

Resolves: Support for Spring WebClient for creating spans/crumbs #1619

💚 How did you test it?

Ported all tests that were available for RestTemplate integration.
Also ran the sample spring boot application with my personal DSN and verified it worked as intended.

📝 Checklist

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

🔮 Next steps

[bruno-garcia]

Looks great! @maciejwalkowiak might have some thoughts as the author of the RestTemplate bits

[marandaneto]

looks good, I'll let @maciejwalkowiak review though since its backend bits.
@yhware thanks for that, would you mind working on the broken CI? this includes running make format to format files, make api to check binary compatibility validator and adding an entry to the changelog.

[marandaneto]

left a comment to fix CI but changes are good LGTM

[maciejwalkowiak]

@yhware thanks a lot for this PR! 🤩 Few small things have to be polished to get it merged. Also, make sure to run ./gradlew apiDump to update files containing public APIs.

[codecov-commenter]

Codecov Report

Merging #1621 (662d95f) into main (1c39818) will decrease coverage by 0.30%.
The diff coverage is 18.91%.

@@             Coverage Diff              @@
##               main    #1621      +/-   ##
============================================
- Coverage     75.93%   75.63%   -0.31%     
- Complexity     2004     2006       +2     
============================================
  Files           202      204       +2     
  Lines          6943     6980      +37     
  Branches        691      692       +1     
============================================
+ Hits           5272     5279       +7     
- Misses         1335     1365      +30     
  Partials        336      336              

Impacted Files	Coverage Δ
...ring/tracing/SentrySpanClientWebRequestFilter.java	0.00% <0.00%> (ø)
...io/sentry/spring/boot/SentryAutoConfiguration.java	98.33% <100.00%> (+0.05%)	⬆️
...try/spring/boot/SentrySpanWebClientCustomizer.java	100.00% <100.00%> (ø)

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[maciejwalkowiak]

Thanks for fixes!