Tracing: don't record HTTP OPTIONS and HEAD transactions

[natikgadzhi]

Summary

This pull request makes it so HTTP OPTIONS and HEAD requests will not be sampled (traced).

Closes #1864. Based on the approach in getsentry/sentry-javascript#5485

Changes

• Adds a check for Rack env http method in capture_exceptions rack app middleware. It felt like the right spot for this, instead of shoving another check in Transaction.set_initial_sample_decision, because it depends directly on an HTTP request, and thus is rather specific to Rack env.
• Adds a changelog entry
• This needs unit tests, but capture_exceptions_spec.rb is scary. I'll write them up tomorrow.

Open questions

• @sl0thentr0py, @st0012, is this the right approach and the right place for this check?
• Another note: this approach ignores the incoming trace. If I'm reading the Javascript implementation correctly, it does the same, since the HTTP method check is the first one in the tracing middleware.

[codecov]

Codecov Report

Merging #2181 (d8891f3) into master (49a628e) will decrease coverage by 30.97%.
The diff coverage is 100.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2181       +/-   ##
===========================================
- Coverage   97.43%   66.47%   -30.97%     
===========================================
  Files         102      100        -2     
  Lines        3817     3749       -68     
===========================================
- Hits         3719     2492     -1227     
- Misses         98     1257     +1159     

Components	Coverage Δ
sentry-ruby	55.75% <ø> (-42.40%)	⬇️
sentry-rails	95.05% <100.00%> (+0.03%)	⬆️
sentry-sidekiq	94.70% <ø> (ø)
sentry-resque	93.65% <ø> (+1.58%)	⬆️
sentry-delayed_job	94.44% <ø> (ø)
sentry-opentelemetry	100.00% <ø> (ø)

Files	Coverage Δ
sentry-rails/lib/sentry/rails/action_cable.rb	100.00% <100.00%> (ø)
...entry-rails/lib/sentry/rails/capture_exceptions.rb	96.77% <100.00%> (+0.22%)	⬆️

... and 56 files with indirect coverage changes

[natikgadzhi]

Added the unit tests, and moved the changelog entry to Unreleased.

[sl0thentr0py]

you'll need the same logic in

sentry-ruby/sentry-rails/lib/sentry/rails/capture_exceptions.rb

Line 34 in 9a22f26

def start_transaction(env, scope)

and

sentry-ruby/sentry-rails/lib/sentry/rails/action_cable.rb

Line 35 in 9a22f26

def start_transaction(env, scope)

[natikgadzhi]

Just passing by here — I'll clean this up today so we can get it merged! Sorry for the delay.

[natikgadzhi]

@sl0thentr0py, thank you for the guidance <3

I've pushed up the code, with two gotchas where I'd love your input and preference:

1. I've duplicated the IGNORED_HTTP_METHODS in the three classes that use it. In theory, we could just put it in module Sentry, and use it with Sentry::IGNORED_HTTP_METHODS, but I think having it in the same file is a bit more readable. Want me to DRY it out?
2. I have not yet added the tests for the Rails and ActionCable pieces. I can get back to this, or we can ship this as is — up to you!

[natikgadzhi]

Hmmmmmmmm

   1) Sentry::Client#event_from_transaction correct dynamic_sampling_context when head SDK
     Failure/Error:
       expect(event.dynamic_sampling_context).to eq({
         "environment" => "development",
         "public_key" => "12345",
         "sample_rate" => "1.0",
         "sampled" => "true",
         "transaction" => "test transaction",
         "trace_id" => transaction.trace_id
       })

       expected: {"environment"=>"development", "public_key"=>"12345", "sample_rate"=>"1.0", "sampled"=>"true", "trace_id"=>"f86126d5bfb14f5d8716c5459fe6495b", "transaction"=>"test transaction"}
            got: {"environment"=>"development", "public_key"=>"12345", "sample_rate"=>"0.5", "sampled"=>"true", "trace_id"=>"f86126d5bfb14f5d8716c5459fe6495b", "transaction"=>"test transaction"}

       (compared using ==)

       Diff:
       @@ -1,6 +1,6 @@
        "environment" => "development",
        "public_key" => "12345",
       -"sample_rate" => "1.0",
       +"sample_rate" => "0.5",
        "sampled" => "true",
        "trace_id" => "f86126d5bfb14f5d8716c5459fe6495b",
        "transaction" => "test transaction",
     # ./spec/sentry/client_spec.rb:183:in `block (3 levels) in <top (required)>'