Fix spans for streaming responses in WSGI based frameworks

[antonpirker]

Fixes spans in streaming responses when using WSGI based frameworks. Only close the transaction once the response was consumed. This way all the spans created during creation of the response will be recorded with the transaction:

• The transaction stays open until all the streaming blocks are sent to the client. (because of this I had to update the tests, to make sure the tests, consume the response, because the Werkzeug test client (used by Flask and Django and our Strawberry tests) will not close the WSGI response)
• A maximum runtime of 5 minutes for transactions is enforced. (like Javascript does it)
• When using a generator to generate the streaming response, it uses the correct scopes to have correct parent-child relationship of spans created in the generator.

People having Sentry in a streaming application will:

• See an increase in their transaction duration to up to 5 minutes
• Get the correct span tree for streaming responses generated by a generator

Fixes #3736

[codecov]

Codecov Report

Attention: Patch coverage is 90.62500% with 6 lines in your changes missing coverage. Please review.

Project coverage is 79.94%. Comparing base (a7c2d70) to head (8574c06).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/integrations/wsgi.py	92.59%	4 Missing ⚠️
sentry_sdk/tracing_utils.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3798      +/-   ##
==========================================
+ Coverage   79.89%   79.94%   +0.05%     
==========================================
  Files         137      137              
  Lines       15385    15421      +36     
  Branches     2611     2614       +3     
==========================================
+ Hits        12292    12329      +37     
- Misses       2222     2223       +1     
+ Partials      871      869       -2     

Files with missing lines	Coverage Δ
sentry_sdk/tracing_utils.py	83.92% <80.00%> (-0.11%)	⬇️
sentry_sdk/integrations/wsgi.py	85.96% <92.59%> (+1.13%)	⬆️

... and 5 files with indirect coverage changes

[sentrivana]

Left a couple of comments. As long as the tests for the various integrations that use the WSGI middleware are happy, I think this looks good.