fix(spotlight): More defensive Django spotlight middleware injection

[BYK]

Turns out settings.MIDDLEWARE does not have to be a list. This causes issues as not all iterables support appending items to them. This PR leverages itertools.chain along with type(settings.MIDDLEWARE) to extend the middleware list while keeping its original type. It also adds a try-except block around the injection code to make sure it doesn't block anything further down in the unexpected case that it fails.

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.31%. Comparing base (f493057) to head (674ca35).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/spotlight.py	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3665      +/-   ##
==========================================
- Coverage   84.32%   84.31%   -0.01%     
==========================================
  Files         133      133              
  Lines       14063    14068       +5     
  Branches     2379     2380       +1     
==========================================
+ Hits        11858    11861       +3     
  Misses       1471     1471              
- Partials      734      736       +2     

Files with missing lines	Coverage Δ
sentry_sdk/spotlight.py	66.66% <87.50%> (+1.09%)	⬆️

... and 1 file with indirect coverage changes