* feat(kms): add admin endpoints for key description and tag updates
Wire the KMS key metadata updates landed at the service layer to the admin
API: POST /v3/kms/keys/{update-description,tag,untag}. Each endpoint gates on
a dedicated KMS action scoped to the key its body names, records a handler-owned
audit entry for both the authorization denial and the outcome, and maps a
backend that cannot update key metadata to 501 rather than 404.
Refs rustfs/backlog#1586 (part of rustfs/backlog#1562)
* fix(admin): audit metadata attempts refused by an unavailable KMS
* test(admin): register the new KMS metadata routes in the matrix
Zhengchao An
81fc61db41