feat(media-proxy): sign attachment URLs and gate origins (#2830)

packages/config/src/MasterConfig.ts

@@ -152,6 +152,9 @@ export interface MasterConfig {
 				token_ttl_secs: number;
 				keep_direct_countries: Array<string>;
 			};
+			attachment_urls: {
+				secrets_base64: Array<string>;
+			};
 		};
 		gateway: {
 			port: number;