Introduce Configuration#validate

[solnic]

This moves checking profiler setup from configuration writers to a new method called validate that is called automatically in Sentry.init after its done setting up configuration instance.

There's also a handy new method for defining simple validations for Configuration:

module Sentry
  class Configuration
    # ...

    validate :traces_sample_rate, optional: true, type: :numeric
    validate :profiles_sample_rate, optional: true, type: :numeric

    # ...
  end
end

The benefit here is that we can validate values that actually need other values in order to be validated, or to perform additional checks like if a 3rd-party dependency is available.

Previously it was not possible because in the moment of validation the configuration was not completed.

Closes #2534

[codecov]

Codecov Report

Attention: Patch coverage is 78.57143% with 6 lines in your changes missing coverage. Please review.

Project coverage is 69.84%. Comparing base (1ee671c) to head (eece6a1).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
sentry-ruby/lib/sentry/configuration.rb	77.77%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2537      +/-   ##
==========================================
+ Coverage   69.32%   69.84%   +0.51%     
==========================================
  Files         125      126       +1     
  Lines        4721     4725       +4     
==========================================
+ Hits         3273     3300      +27     
+ Misses       1448     1425      -23     

Components	Coverage Δ
sentry-ruby	60.78% <66.66%> (+0.78%)	⬆️
sentry-rails	97.48% <100.00%> (+0.71%)	⬆️
sentry-sidekiq	95.52% <100.00%> (-1.56%)	⬇️
sentry-resque	92.64% <ø> (-0.22%)	⬇️
sentry-delayed_job	95.65% <ø> (ø)
sentry-opentelemetry	100.00% <ø> (+0.68%)	⬆️

Files with missing lines	Coverage Δ
sentry-ruby/lib/sentry-ruby.rb	67.71% <100.00%> (+0.14%)	⬆️
sentry-ruby/lib/sentry/configuration.rb	85.86% <77.77%> (-0.02%)	⬇️

... and 24 files with indirect coverage changes

[solnic]

@sl0thentr0py @st0012 what do you think about this approach? If you could give me a 👍🏻 I'd love to continue and make a tiny API for defining validations for our settings so that we can have it work consistently for all values. Seems like a nice improvement and it'd fix the issue we're facing with profiler setup.

[sl0thentr0py]

yes sure, this is definitely an improvement

[solnic]

Please ignore jruby failures, currently jruby doesn't bundle on our CI. There's #2536 pending PR that's meant to fix it.

[sl0thentr0py]

let's ignore jruby ci for now, I'm fixing that separately