* feat(policy): add built-in KMS role policies
KMSKeyAdministrator, KMSKeyUser and KMSAuditor ship as canned identity
policies so operators can express KMS role separation without hand-writing
the resource grammar. They grant only kms actions, so they compose with an
existing data-plane policy, and none of them confers kms:Configure,
kms:ServiceControl, kms:ClearCache, kms:Backup or kms:Restore.
* docs(kms): document per-key KMS authorization and the role templates
* test(kms): add an end-to-end negative authorization matrix
Covers the admin and SSE-KMS planes for a wrong identity, a wrong key, a
wrong action and an explicit Deny, each preceded by a positive control so a
denial cannot be an unpropagated policy. SSE-S3 and unencrypted objects are
asserted to stay exempt.
* test(replication): pin the SSE-KMS contract with per-key authorization on
The replication worker carries no request identity, so it must stay exempt
from SSE-KMS key authorization. Running the existing contract with the
switch enabled makes a regression in that exemption visible here.
