Remove version from docker as it is deprecated

[Eduardo-Morales-Alberti]

Warning:

time="2024-03-22T08:03:03+01:00" level=warning msg="/var/lib/jenkins/workspace/schaer-schaer_tests_PR-462/docker-compose.yml: version is obsolete"
time="2024-03-22T08:03:03+01:00" level=warning msg="/var/lib/jenkins/workspace/schaer-schaer_tests_PR-462/jenkins/docker-compose.override.yml: version is obsolete"

Solution:
mailcow/mailcow-dockerized#5797 (comment)

Please remove the version line from the docker-compose.yml file and verify that everything still works correctly on your end. Docker has made this line obsolete, which is likely the reason you're facing this issue

[omarlopesino]

Adding the official information to the pull request to the information https://docs.docker.com/compose/compose-file/04-version-and-name/ . As edu and the issue referenced mentions the version attribute is not neccesary anymore and only used for backwards compatibility. We can remove it, and if any project needs it, it can be manually added to support older versions.

Merging, thanks!