Find which end-to-end tests can run side by side #869

The end-to-end suite runs one test at a time, and it took 12 min 49 s to 13 min 11 s of every green E2E Tests run on main between 2026-11-04 15:04Z and 2026-11-05 10:02Z, for example run 42007412565.

The serial run is a decision, and two reasons for it are written down.

Some tests already say that they must run alone, with concurrent: false, for example gateway-invalid-certificate.

The question this raises: which tests share no fixture and need no warm proxy, so that they can run beside each other while the rest stay serial?

Proposed scope

• For each test, record what it shares: the ipam-e2e-* namespaces, cluster-scoped fixtures, or the shared data plane.
• Mark each test that shares something concurrent: false, and let the rest run two or three at a time.
• Measure the suite on repeated runs, and look for new flakes.

Non-goals

• Waits that come from the product, not from the test.
• The hostname tests' teardown (Hostname test teardown runs too long #358).

Acceptance criteria

• Each test that must run alone says why, beside its concurrent: false.
• The suite passes on repeated runs on main with tests side by side, with no new flake.
• The suite is shorter, or this issue records why it stays serial.