[breaking] Enable Django cache_spans by default

[BYK]

This reverts commit 955108e (#3791) and simply enables cache_spans by default..

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.56%. Comparing base (4d64c4e) to head (42c3d41).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3994   +/-   ##
=======================================
  Coverage   79.55%   79.56%           
=======================================
  Files         140      140           
  Lines       15512    15509    -3     
  Branches     2628     2628           
=======================================
- Hits        12341    12339    -2     
  Misses       2335     2335           
+ Partials      836      835    -1     

Files with missing lines	Coverage Δ
sentry_sdk/integrations/django/__init__.py	81.48% <ø> (ø)
sentry_sdk/integrations/django/caching.py	92.70% <100.00%> (-0.23%)	⬇️

... and 1 file with indirect coverage changes

[antonpirker]

The changes look good.

We will probably release this with version 3.0 of the SDK. (which will be done in a couple of weeks/months)

[antonpirker]

just put this here that not accidentally someone merges this. see my other review above for the real review :-)