Add support for async methods in Spring MVC.

[maciejwalkowiak]

📜 Description

Add support for async methods in Spring MVC.

💡 Motivation and Context

Using the same technique as for coroutines and Webflux, using a task decorator propagates Hub with Scope to the executing thread in async tasks.

Fixes #1226
Fixes #1107

Sample how it can be used: https://github.com/maciej-scratches/sentry-spring-mvc-async-controller/blob/master/src/main/java/com/example/springasynccontroller/SpringAsyncControllerApplication.java

💚 How did you test it?

Integration tests, sample project.

📝 Checklist

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

🔮 Next steps

Add reference docs.

[codecov-commenter]

Codecov Report

Merging #1652 (d0421e0) into main (733f0e0) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #1652      +/-   ##
============================================
+ Coverage     75.74%   75.77%   +0.02%     
- Complexity     2016     2019       +3     
============================================
  Files           206      207       +1     
  Lines          7037     7045       +8     
  Branches        699      699              
============================================
+ Hits           5330     5338       +8     
  Misses         1369     1369              
  Partials        338      338              

Impacted Files	Coverage Δ
...ain/java/io/sentry/spring/SentryTaskDecorator.java	100.00% <100.00%> (ø)

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[marandaneto]

@maciejwalkowiak lets document this too :)