Run full e2e tests in pipeline tier 3 and above

From Draft to Ready

• The follow-up of Simplify rules for package-and-test-ee and trigger-omnibus-env is merged (it was reverted)
  • It will probably create git conflicts otherwise.
• Ensure that we ran the latest pipeline tier before an MR is merged is closed
  • Pipelines Safety: Without this issue, we could merge merge requests without having run anything above tier-1 (including E2E tests)
• Trigger a new pipeline after each increasing tier transition is closed
  • Pipelines user-friendliness: Not strictly needed, but will greatly improve the first experience with pipeline tiers (otherwise, people would have to trigger pipelines manually, only discovering this after failing the final merge train checks)

What does this MR do and why?

Moves full E2E pipelines to run in pipelinetier-3 (i.e. when all approvals for an MR were given).

We keep the GDK tests running after an MR was first approved (i.e. right after pipelinetier-1, could be pipelinetier-2 or pipelinetier-3 depending on the number of approvals needed on the MR).

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Related to #459977 (closed)