feat(services): add getAll function to mysql service

This commit adds a new `getAll` function in the `mysql.service.ts` file, which retrieves all categories from the database. It executes a SQL query and includes error handling that either resolves with an array of category objects or rejects with an Error object.

BREAKING-CHANGE: #6
Signed-off-by: Mathis <yidhra@tuta.io>

src/services/mysql.service.ts

@@ -402,7 +402,25 @@ const MySqlService = {
 				}
 			})
 		},
-
+		/**
+		 * Retrieves all categories from the database.
+		 *
+		 * @param {MysqlHandler} handler - The MySQL handler used for executing the query.
+		 *
+		 * @return {Promise<Array<IDbCategory>>} - A promise that resolves with an array of category objects from the database.
+		 *                                       - The category objects are of type IDbCategory.
+		 *                                       - If an error occurs, the promise will be rejected with an Error object.
+		 */
+		getAll(handler: MysqlHandler) {
+			return new Promise((resolve, reject) => {
+				const _sql = "SELECT * FROM `categories`";
+				try {
+					resolve(handler.query(_sql) as unknown as Array<IDbCategory>);
+				} catch (err: unknown) {
+					reject(err as Error);
+				}
+			});
+		}
 	}
 }