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/charts/user/reactions.ts

@@ -10,6 +10,8 @@ export const meta = {
 		'ja-JP': 'ユーザーごとの被リアクション数のチャートを取得します。'
 	},
 
+	tags: ['charts', 'users', 'reactions'],
+
 	params: {
 		span: {
 			validator: $.str.or(['day', 'hour']),
@@ -34,7 +36,14 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		}
-	}
+	},
+
+	res: {
+		type: 'array',
+		items: {
+			type: 'object',
+		},
+	},
 };
 
 export default define(meta, async (ps) => {