remove CI module and add a dependency on datadog-ci gem

[anmarchenko]

What does this PR do?
Phase 1 of the CI migration:

• remove the CI module, corresponding specs and sigs
• add datadog-ci to the gemspec as runtime dependency
• remove cucumber appraisals
• remove minitest and rspec deps from the contrib appraisal
• update lockfiles
• add datadog-ci to lib-injection scripts

Motivation:
Remove code duplication between gems

Additional Notes:
Not that it is a new runtime dependency I changed host_inject.rb script to install datadog-ci here:
https://github.com/DataDog/dd-trace-rb/pull/3128/files#diff-112f50906c11b7190b1561f372bd7298abe32cda4be0054ced470a584cffb7d3R66

Is there a way to test this? cc @TonyCTHsu

How to test the change?

git clone https://github.com/DataDog/test-environment

cd test-environment

yarn

cd dd-trace-rb/jekyll
bundle add ddtrace --git "https://github.com/DataDog/dd-trace-rb.git" --branch "anmarchenko/migrate_ci_phase_1" --skip-install
bundle install --path .bundle
cd ../..

yarn test dd-trace-rb/jekyll.test.js

cd dd-trace-rb/devdocs
bundle add ddtrace --git "https://github.com/DataDog/dd-trace-rb.git" --branch "anmarchenko/migrate_ci_phase_1" --skip-install
bundle install --path .bundle
cd ../..

yarn test dd-trace-rb/devdocs.test.js

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[codecov-commenter]

Codecov Report

Merging #3128 (430aa03) into master (7ab178d) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3128      +/-   ##
==========================================
- Coverage   98.17%   98.14%   -0.03%     
==========================================
  Files        1326     1281      -45     
  Lines       75575    73715    -1860     
  Branches     3506     3423      -83     
==========================================
- Hits        74192    72347    -1845     
+ Misses       1383     1368      -15     

see 46 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[marcotc]

Looking good! 👍

[TonyCTHsu]

Perhaps we should change gemspec to add runtime dependency for ci ?

[anmarchenko]

@TonyCTHsu didn't I add it to gemspec? I think it is here https://github.com/DataDog/dd-trace-rb/pull/3128/files#diff-8b1801e03e9a166eea28410efc558b347e0b4a3bc03ab6c7283afa4479e88756R72

and all the regenerated gemfiles for appraisals now show datadog-ci (0.1.0)

[TonyCTHsu]

🕶️ I was blind