Update `docker-compose.workspace.yml` & `.env` for easier setup

[KaKi87]

Hi,

This PR :

• changes ONLYOFFICE image tags (except onlyoffice/elasticsearch) with latest in docker-compose.workspace.yml ;
• adds a TODO in it and in .env to remind the user to fill MAIL_SERVER_HOSTNAME ;
• uncomments a line to solve an issue by default ;
• therefore closes #203.

Thanks

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