feat(discover): Add more tags for error reason

[narsaynorath]

A lot of other errors are being eaten up as timeouts (e.g. rate limiting). Add the class name as a tag so we have better insight into what broke.

Note: I also think ParseError is the wrong exception to be throwing here, but the existing behaviour is to throw that. It might make more sense to break these out further and e.g. throw a 429 for a rate limit issue.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/sentry/api/utils.py	66.66%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #78489   +/-   ##
=======================================
  Coverage   78.10%   78.10%           
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  Files        7076     7076           
  Lines      311942   311945    +3     
  Branches    50939    50940    +1     
=======================================
+ Hits       243648   243653    +5     
+ Misses      61940    61936    -4     
- Partials     6354     6356    +2