Add a --base-issue-labels flag to add custom flags to flaky test issues

Context

• Related to gitlab-org/gitlab#428768 (closed)
• Closes #45 (closed)

What does this MR do and why?

Add the --base-issue-labels flag to be able to add custom flags when using exe/flaky-test-issues.

How to set up and validate locally

# 51263763 is the project ID of https://gitlab.com/ddieulivol/sandbox/-/issues/
exe/flaky-test-issues \
  --input-files spec/gitlab_quality/test_tooling/report/fixtures/rspec-reports/flaky/rspec-retry-5258318483.json \
  --project 51263763 \
  --base-issue-labels "from_new_rspec_process, from_rspec_retry_gem" \
  --token "${GITLAB_API_PRIVATE_TOKEN}"

Example of a flaky test issue -> ddieulivol/sandbox#56 :

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.