Extract thread control logic into a new ThreadedPeriodicWorker class

[st0012]

Instead of letting BackpressureMonitor, SessionFlusher, and Metrics::Aggregator handle their own threading logic, we can extract that into a new class that can be reused by all of them.

Closes #2261

#skip-changelog

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.73%. Comparing base (6cdb1fc) to head (309661e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2304      +/-   ##
==========================================
+ Coverage   98.72%   98.73%   +0.01%     
==========================================
  Files         202      203       +1     
  Lines       13301    13274      -27     
==========================================
- Hits        13131    13106      -25     
+ Misses        170      168       -2     

Components	Coverage Δ
sentry-ruby	99.12% <100.00%> (+0.01%)	⬆️
sentry-rails	97.37% <ø> (ø)
sentry-sidekiq	96.98% <ø> (ø)
sentry-resque	96.76% <ø> (ø)
sentry-delayed_job	98.91% <ø> (ø)
sentry-opentelemetry	100.00% <ø> (ø)

Files	Coverage Δ
sentry-ruby/lib/sentry-ruby.rb	96.58% <100.00%> (+0.01%)	⬆️
sentry-ruby/lib/sentry/backpressure_monitor.rb	100.00% <100.00%> (+2.27%)	⬆️
sentry-ruby/lib/sentry/metrics/aggregator.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/session_flusher.rb	100.00% <100.00%> (+2.00%)	⬆️
sentry-ruby/lib/sentry/threaded_periodic_worker.rb	100.00% <100.00%> (ø)
...ntry-ruby/spec/sentry/backpressure_monitor_spec.rb	100.00% <100.00%> (ø)
sentry-ruby/spec/sentry/metrics/aggregator_spec.rb	100.00% <100.00%> (ø)
sentry-ruby/spec/sentry/session_flusher_spec.rb	100.00% <100.00%> (ø)

[sl0thentr0py]

ty! <3