Update CI to label-driven testing

[Micky774]

Description

With this PR, testing is mediated by labels such as: ci-level {1, 2, 3}. No tests will be run without at least one label present. At any given time, the highest-level label will take precedence, and only its corresponding level of tests will be run. The workflow triggers on labeling, unlabeling, and pushing commits. When removing a label, the workflow will check to see if there are any labels remaining and if there are, it will dispatch to the highest of them.

Fixes # (issue)

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Infra/Build change
• Code refactoring

Changes

Please list the changes introduced in this PR:

• Change A
• Change B

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[ipanfilo]

Maybe make approach more generic - ci_level% label specifies CI level to use.