s3: add Scality (RING / ARTESCA) provider

Add Scality as an S3 provider covering both Scality RING (S3 Connector)
and ARTESCA, which share the same CloudServer + Vault S3 implementation.

The only quirk required is force_path_style: both products support
path-style addressing, and virtual-hosted style needs wildcard DNS that
on-prem deployments usually lack.

backend/s3/provider/Scality.yaml

@@ -0,0 +1,8 @@
+name: Scality
+description: Scality (RING / ARTESCA)
+region: {}
+endpoint: {}
+location_constraint: {}
+acl: {}
+quirks:
+  force_path_style: true # RING and ARTESCA support path-style; virtual-hosted style needs wildcard DNS which on-prem clients often lack