[SDTEST-228] Auto instrumentation

[anmarchenko]

What does this PR do?
Allows Ruby test runs to be autoinstrumented without code changes (via RUBYOPT env variable or datadog-ci CLI).

Example using RUBYOPT:
RUBYOPT="-rbundler/setup -rdatadog/ci/auto_instrument" bundle exec rake test

Example using ddcirb CLI tool:
bundle exec ddcirb exec bundle exec rake test

Motivation
Easier onboarding

How to test the change?
There are integration tests provided, also tested using a number of open source projects' forks

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 78.94737% with 28 lines in your changes missing coverage. Please review.

Project coverage is 98.52%. Comparing base (9c8d52b) to head (bdb6589).

Files with missing lines	Patch %	Lines
lib/datadog/ci/contrib/instrumentation.rb	60.78%	20 Missing ⚠️
lib/datadog/ci/cli/command/exec.rb	64.28%	5 Missing ⚠️
lib/datadog/ci/cli/cli.rb	75.00%	1 Missing ⚠️
lib/datadog/ci/contrib/integration.rb	75.00%	1 Missing ⚠️
lib/datadog/ci/test_retries/strategy/retry_new.rb	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #259      +/-   ##
==========================================
- Coverage   98.77%   98.52%   -0.26%     
==========================================
  Files         293      298       +5     
  Lines       13957    14079     +122     
  Branches      669      680      +11     
==========================================
+ Hits        13786    13871      +85     
- Misses        171      208      +37     

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