Added documentation to delete account

Delete User Cccount

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1. Delete email account and data

    - login to mail.$DOMAIN

    - click on domain list

    - select the correct domain

    - search for the username on the top right

    - delete the correct account

2. delete nextcloud files and data

    - Note: we need to delete this manually at the moment, maybe it will work automatically with the user_external plugin.

    - `ssh user@$DOMAIN`

    - `cd /mnt/repo-base/`

    - `sudo rm -r volumes/nextcloud/data/user@$DOMAIN/`

    - `sudo docker-compose exec mariadb mysql -u root -p`

    - `use nextcloud;`

    - `DELETE FROM calendars WHERE principaluri='principals/users/user@$DOMAIN';`

    - `DELETE FROM addressbooks WHERE principaluri='principals/users/user@$DOMAIN';`

4. onlyoffice data

    - go to [https://office.$DOMAIN/products/people/#sortorder=ascending](https://office.$DOMAIN/products/people/#sortorder=ascending)

    - search for the username

    - click on the arrow at the far right and press "Delete profile"