rgw/logging: use assumed-role ARN as Requester for STS requests

rgw/logging: use assumed-role ARN as Requester for STS requests

When a request is made with STS temporary credentials, the bucket logging
Requester field was being set to the underlying user ID instead of the
assumed-role ARN. Per the AWS S3 server-access-log spec, the Requester
field should contain the assumed-role ARN (e.g.
arn:aws:sts::<account>:assumed-role/<role>/<session>) for STS-credentialed
requests.

Detect TYPE_ROLE identities via s->auth.identity->get_identity_type() and
use the ARN returned by Identity::get_caller_identity() (already
implemented by RoleApplier in the expected AWS format) instead of falling
straight through to s->user->get_id(). Existing behavior for account- and
user-scoped requests is unchanged.

Fixes: https://tracker.ceph.com/issues/71742
Signed-off-by: Shree Jejurikar <shree.jejurikar@gmail.com>