Add Metrics API and aggregator

[sl0thentr0py]

• new Sentry::Metrics module with 4 apis that map to the new 4 Sentry::Metrics::Metric classes
  • increment - simple counter
  • distribution - array of observations
  • gauge - statistics (last/min/max/sum/count)
  • set - unique values
• new Sentry::Metrics::Aggregator that starts a thread that flushes pending metric buckets in 5 second intervals
  • buckets are a nested hash of timestamp (rolled to 10 second intervals) -> metric keys -> actual metric instance
  • there is a random flush_shift once per startup to create jittering
  • flushable buckets are sent in a new statsd type envelope that is not json so made a small change to the Envelope::Item
  • tag key/values are sanitized for unicode/special characters according to the two regexes

Reference spec - https://develop.sentry.dev/sdk/metrics/

part of #2246

[codecov[bot]]

Codecov Report

Merging #2247 (0e87bab) into master (478c4cf) will increase coverage by 0.12%. The diff coverage is 99.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2247      +/-   ##
==========================================
+ Coverage   97.41%   97.54%   +0.12%     
==========================================
  Files         102      110       +8     
  Lines        3828     4026     +198     
==========================================
+ Hits         3729     3927     +198     
  Misses         99       99              

Components	Coverage Δ
sentry-ruby	98.23% <99.50%> (+0.08%)	:arrow_up:
sentry-rails	95.05% <ø> (ø)
sentry-sidekiq	94.70% <ø> (ø)
sentry-resque	92.30% <ø> (+1.53%)	:arrow_up:
sentry-delayed_job	95.60% <ø> (ø)
sentry-opentelemetry	100.00% <ø> (ø)

Files	Coverage Δ
sentry-ruby/lib/sentry-ruby.rb	96.56% <100.00%> (+0.12%)	:arrow_up:
sentry-ruby/lib/sentry/configuration.rb	98.80% <100.00%> (+0.01%)	:arrow_up:
sentry-ruby/lib/sentry/envelope.rb	97.95% <100.00%> (ø)
sentry-ruby/lib/sentry/metrics.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/metrics/configuration.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/metrics/counter_metric.rb	100.00% <100.00%> (ø)
...try-ruby/lib/sentry/metrics/distribution_metric.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/metrics/gauge_metric.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/metrics/metric.rb	100.00% <100.00%> (ø)
sentry-ruby/lib/sentry/metrics/set_metric.rb	100.00% <100.00%> (ø)
... and 3 more

... and 1 file with indirect coverage changes

[sl0thentr0py]

will add unit lists in separate PR

[sl0thentr0py]

@st0012 im gonna start merging these because we want to ship this week. If you have things you want changed, feel free to leave reviews anyway, I can change them separately.