refactor(config): vigie config and test file definition clarification

[qboileau]

What changed in a test file

Replace cluster with tier.

 suite: apply-tier matcher showcase
+tier: e2e # optional default to template valid values are template|apiserver|e2e

-cluster:
-  backend: kubeconfig

 defaults:
   release:
     name: myapp

Now matchers expect capabilities that can be provided by tier ladder.

.vigie.yaml also changed

 test:
   testsDir: tests
+  cluster:
+    envtest: { kubeVersion: 1.36.1 }
+    kind:    { binary: "", extraArgs: [] }
+    kubeconfig: { path: /home/me/.kube/config }
-testApply:
-  cluster:
-    type: envtest

One test: block instead of a test:/testApply: split, with per-backend settings. A stale testApply: fails at load, naming its line and new home.