Audit policy metadata-only rule should include `serviceaccounts/token` resource

[liggitt]

The following files reference a metadata-only audit policy in order to prevent logging request/response contents for sensitive resources:

• https://github.com/kontena/pharos-cluster/blob/master/lib/pharos/resources/audit/policy.yml

A recent Kubernetes bugfix means that audit-logging of subresource requests which previously failed will now log successfully. The serviceaccounts/token subresource responds to TokenRequest API calls with a newly minted service account token.

The serviceaccounts/token resource should also be included in the metadata-only audit policy if credentials are not intended to appear in the audit log:

- group: "" # core
  resources: ["secrets", "configmaps", "serviceaccounts/token"]