Move the aws_sdk_s3 client construction out of bucket_target_sys into
bucket/remote_s3_client.rs: endpoint assembly, credential provider,
path-style selection, custom CA / skip-TLS transports and the outbound
SSRF gate now build from a neutral RemoteS3EndpointSpec so replication
targets and the upcoming on-demand migration source client share one
policy. Replication builds its client through From<&BucketTarget>; the
gate keeps its relaxed semantics (private allowed, loopback only behind
RUSTFS_REPLICATION_ALLOW_LOOPBACK_TARGET) verbatim. The builder also
gains optional connect/read timeouts and a User-Agent suffix
interceptor, both unset for replication.
Refs rustfs/backlog#2149
overtrue
6b8c1f0776