helm: helm test: add lint rule for incorrect helm test hook types

When I purposely supply an incorrect/unsupported test hook, I’d expect to see a subsequent helm test invocation supply an error specific to this situation.

Changing the docs/examples/nginx/templates/service-test.yaml to the following:

apiVersion: v1
kind: Pod
metadata:
  name: "{{.Release.Name}}-service-test"
  annotations:
    "helm.sh/hook": test-pass
spec:
  containers:
    - name: curl
      image: radial/busyboxplus:curl
      command: ['curl']
      args:  [ '{{ template "fullname" .}}:{{default 80 .Values.httpPort}}' ]
  restartPolicy: Never

(Only test hooks supported as of this writing are test-success and test-failure, as seen here)

After example chart install:

$ bin/helm test needled-starfish
Error: no tests found