Raise version of MySQL docker image from 5.7 to 8

New CRM Skeleton installation should use MySQL 8.0.

The preliminary end of support for MySQL 5.7 in CRM is scheduled for
April 2022. Check [REMP Technical news - v 0.35.0][1] for more details.

[1]: https://remp2020.github.io/#25-oct-2021-new-version-of-crm-is-available-0350.

docker-compose.yml

@@ -34,7 +34,7 @@ services:
     restart: "unless-stopped"
 
   mysql:
-    image: "mysql:5.7"
+    image: "mysql:8.0"
     volumes:
       - "mysql-data:/var/lib/mysql"
       - ".:/data"