Introduce OpenAPI specs (#4351)

* wip

* wip

* wip

* Update index.ts

* Update gen-openapi-spec.ts

* Update api.ja-JP.md

* Fix

* Improve doc

* Update gen-openapi-spec.ts

* Update redoc.html

* Improve doc

* Update gen-openapi-spec.ts

* Improve doc

* Update CHANGELOG.md

src/server/api/endpoints/notes/replies.ts

@@ -11,6 +11,8 @@ export const meta = {
 		'en-US': 'Get replies of a note.'
 	},
 
+	tags: ['notes'],
+
 	requireCredential: false,
 
 	params: {
@@ -32,7 +34,14 @@ export const meta = {
 			validator: $.optional.num.min(0),
 			default: 0
 		},
-	}
+	},
+
+	res: {
+		type: 'array',
+		items: {
+			type: 'Note',
+		},
+	},
 };
 
 export default define(meta, async (ps, user) => {