Add ~"test-health::" labels to existing issues with flakiness/slowness/failure::new labels with a one-off migration

Context

In gitlab-org/ruby/gems/gitlab_quality-test_tooling#88 (closed), we added the test-health:failures / test-health:pass-after-retry test-health:slow labels to new issues we'll create.

The idea is to be able to uniquely identify a test health problem amongst all of the issues we create. This was not easily possible before those labels.

All new/updated issues will have those labels, BUT the existing issues that won't be updated right away won't have them.

Goal

Add the ~"test-health:*" label on test health issues that should have it.

Technical implementation

Write a one-off migration that would be applied once the latest release of the gitlab_quality-test_tooling is in use in gitlab-org/gitlab.