Add rule and checks to validate no test cross-imports are performed

[cbeauchesne]

Motivation

A test file should not import anything from another test file, as it'll defeat the CI orchestrator mechanism. This rule is easy to miss (8 occurences so far in the test base)

Changes

• add PR rule for AI
• Add generic rule for AI
• Add a test in test_the_test

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

🚀 Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

.cursor/rules/pr-review.mdc                                             @DataDog/system-tests-core
.cursor/rules/repository-structure.mdc                                  @DataDog/system-tests-core
tests/test_the_test/test_conventions.py                                 @DataDog/system-tests-core

[datadog-datadog-prod-us1-2]

⚠️ Warnings

🚦 2 Pipeline jobs failed

Testing the test | Test the test     

Testing the test | all-jobs-are-green     

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