Create fail-fast mechanism on MR pipeline

Add rspec fail-fast job
- This job runs rspec on test files detected by
  the job `detect-tests`.

Add fail-pipeline-early job
- This job cancels the current pipeline in order
  to provide fast feedback upon test failure.
  This happens when the `rspec fail-fast` jobs has failed.

Add toggle to enable `rspec fail-fast`
- The rspec-fail-fast and fail-pipeline-early jobs
  will only be created if the RSPEC_FAIL_FAST_ENABLED variable
  is "true".
- Using this flag, we can experiment with this pipeline
  change with more control.

Add option to skip rspec fail-fast
- Using MR title SKIP RSPEC FAIL-FAST
- Using dont-interrupt-me job