Add S3 encryption

crates/pile-config/src/lib.rs

@@ -84,6 +84,9 @@ pub enum Source {
 		/// How to group files into items in this source
 		#[serde(default)]
 		pattern: GroupPattern,
+
+		/// If provided, assume objects are encrypted with this secret key.
+		encryption_key: Option<String>,
 	},
 }