Replace OpenSearch license header with Wazuh's AGPLv3 header

[QU3B1M]

Description

Add new license header for the plugins source code, and apply it using the spotless tool. It also includes some minor styling modifications.

Applied license header

/*
 * Copyright (C) 2024, Wazuh Inc.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

Issues Resolved

Resolves #181

[AlexRuiz7]

LGTM