Add RestClient instrumentation for SSRF detection

[y9v]

What does this PR do?
It adds SSRF detection for rest-client gem.

To enable rest-client AppSec instrumentation:

Datadog.configure do |c|
  c.tracing.enabled = true
  c.tracing.instrument :rack

  c.appsec.enabled = true
  c.appsec.instrument :rest_client
end

Motivation:
We want to add SSRF detection to more http client libraries.

Change log entry
Yes. AppSec: Add detection of Server-Side Request Forgery attacks for rest-client http client.

Additional Notes:
None.

How to test the change?
CI and app-generator (rails-ssrf application)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-24 12:13:50

Comparing candidate commit a632a16 in PR branch appsec-add-rest-client-instrumentation with baseline commit 2d817ff in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 31 metrics, 2 unstable metrics.

[datadog-datadog-prod-us1]

Datadog Report

Branch report: appsec-add-rest-client-instrumentation
Commit report: a632a16
Test service: dd-trace-rb

✅ 0 Failed, 20612 Passed, 1375 Skipped, 3m 21.69s Total Time

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.67442% with 3 lines in your changes missing coverage. Please review.

Project coverage is 97.72%. Comparing base (2d817ff) to head (a632a16).

Files with missing lines	Patch %	Lines
.../datadog/appsec/contrib/rest_client/integration.rb	90.90%	2 Missing ⚠️
lib/datadog/appsec/contrib/rest_client/patcher.rb	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4424      +/-   ##
==========================================
- Coverage   97.73%   97.72%   -0.01%     
==========================================
  Files        1363     1368       +5     
  Lines       83309    83438     +129     
  Branches     4217     4220       +3     
==========================================
+ Hits        81418    81543     +125     
- Misses       1891     1895       +4     

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[Strech]

LGTM

P.S I would consider few adjustments to tests and ask Tony about the Matrixfile