Log errors happened in BackgroundWorker#perform

[st0012]

I assumed the block passed to BackgroundWorker#perform should already handle exceptions (e.g. Client#send_event). But #1618 showed it's not entirely true. So this PR adds exception logging to background worker and provide a safer approach to monkey patch its method.

Closes #1618

[codecov-commenter]

Codecov Report

Merging #1624 (5515876) into master (1f96dce) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1624      +/-   ##
==========================================
- Coverage   98.50%   98.49%   -0.02%     
==========================================
  Files         133      133              
  Lines        7382     7394      +12     
==========================================
+ Hits         7272     7283      +11     
- Misses        110      111       +1     

Impacted Files	Coverage Δ
sentry-rails/lib/sentry/rails/background_worker.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/background_worker.rb	100.00% <100.00%> (ø)
sentry-ruby/spec/sentry/background_worker_spec.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/breadcrumb.rb	95.65% <0.00%> (-4.35%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1f96dce...5515876. Read the comment docs.