Add new trace_propagation_targets configuration

[sl0thentr0py]

to set outgoing targets for trace header propagation according to https://develop.sentry.dev/sdk/performance/#tracepropagationtargets
closes #2078

[codecov]

Codecov Report

Patch coverage: 61.53% and no project coverage change.

Comparison is base (7764384) 83.23% compared to head (e651d76) 83.23%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2079   +/-   ##
=======================================
  Coverage   83.23%   83.23%           
=======================================
  Files         119      119           
  Lines        5665     5671    +6     
=======================================
+ Hits         4715     4720    +5     
- Misses        950      951    +1     

Files Changed	Coverage Δ
sentry-ruby/lib/sentry/net/http.rb	29.78% <37.50%> (+0.89%)	⬆️
sentry-ruby/lib/sentry/configuration.rb	84.61% <100.00%> (+0.19%)	⬆️
...try-ruby/lib/sentry/interfaces/single_exception.rb	65.71% <100.00%> (+1.00%)	⬆️

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