Bump up the minimum required MySQL version (#25465)

MySQL 5.7 is at end of life.

https://mattermost.atlassian.net/browse/MM-55589

```release-note
We bump up minimum MySQL version to be 8.0.0
```


Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Ibrahim Serdar Acikgoz <serdaracikgoz86@gmail.com>

server/build/docker/mysql.conf.d/custom.cnf

@@ -1,6 +1,7 @@
 [mysqld]
 bind-address = 0.0.0.0
 
+default-authentication-plugin=mysql_native_password
 log-output = NONE
 slow-query-log = 0
 innodb_flush_log_at_trx_commit = 2