Add onlyoffice stack for local slim Murena workspace

Description

Adding only office into local slim Murena Workspace stack by default. In order to reduce the number of container we will reuse the existing postgresql container.

usage	admin console

Tasks

number	task	help/example
1	Install nextcloud onlyoffice app by default	73721531
2	Be able to configure only office on nextcloud with environment variables prefixed by `ONLYOFFICE_`	https://gitlab.e.foundation/e/infra/ecloud/nextcloud/-/blob/slim/config/nextcloud/pgsql_ssl.config.php
3	Patch postgresql container init to make onlyoffice db	https://hub.docker.com/_/postgres#initialization-scripts
4	Add onlyoffice services into docker-compose.local.yml	https://github.com/ONLYOFFICE/Docker-DocumentServer/blob/master/docker-compose.yml
5	Add 3 default relevant samples (doc, xls, ppt)	https://gitlab.e.foundation/e/infra/ecloud/nextcloud/-/blob/slim/slim.Dockerfile#L28

Tests

Ensure that we can run the local instance with following the default README.
User can load any kind of onlyoffice documents just after a fresh install of slim Murena Workspace without any admin action.
User can edit and save any kind of onlyoffice documents.
If any environment variable are set related to ONLYOFFICE_ the onlyoffice config will be the one provided by default by onlyoffice.
From main docker-compose only new environment variable should be added.
OnlyOffice can by reached with http (local) or https (staging and production) environment

Guidelines

Please follow our guideline before to submit a merge request. At least one commit per task is required.

External references

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