mysql: Fix "mbind: Operation not permitted" warning"

https://github.com/docker-library/mysql/issues/303#issuecomment-643154859

src/services.js

@@ -1184,6 +1184,7 @@ function startMysql(existingInfra, callback) {
                     -e CLOUDRON_MYSQL_ROOT_PASSWORD=${rootPassword} \
                     -v "${dataDir}/mysql:/var/lib/mysql" \
                     --label isCloudronManaged=true \
+                    --cap-add SYS_NICE \
                     --read-only -v /tmp -v /run "${tag}"`;
 
         async.series([