fix(yaml): Add extensions?: string[] to RollupYamlOptions types (#1506)

* add extensions?: string[] to RollupYamlOptions

* test extension option in yaml/test/types.ts

Author: janosh

packages/yaml/test/types.ts

@@ -19,7 +19,8 @@ const config: RollupOptions = {
         }
 
         return data;
-      }
+      },
+      extensions: ['.yaml', '.yml', '.cff']
     })
   ]
 };

packages/yaml/types/index.d.ts

@@ -37,6 +37,13 @@ interface RollupYamlOptions {
    * @default 'single'
    */
   documentMode?: 'single' | 'multi';
+
+  /**
+   * File extensions to process. Useful if you have files that contain YAML but do not have a
+   * `.yaml` or `.yml` extension.
+   * @default ['.yaml', '.yml']
+   */
+  extensions?: string[];
 }
 
 /**