Added support for setting the timezone in Docker

[tobia]

Summary

Several functions in Collabora Online depend on the server timezone setting.
The most common is possibly the rendering of dates and times using the <text:date>
tag in order to include the current date and time in the header or footer of documents.

Unfortunately current docker images do not provide any means to change the timezone
from the default UTC. Linux docker users should be able to mount the system's /etc/localtime
and similar system files, but this is a hack, does not support users in other platforms, and
does not seem to work in recent versions of the docker images.

This commit adds the the tzdata package to Ubuntu-based docker builds and the
timezone package to openSUSE builds. This allows docker users to run the containers
with a custom timezone by simply passing a TZ env variable. For example:

docker run -e TZ=Australia/Sydney collabora/code

Docker images based on Debian already include the tzdata package, therefore no change is needed.

Checklist

• Code is properly formatted
• All commits have Change-Id
• I have run tests with make check
• I have issued make run and manually verified that everything looks okay
• Documentation (manuals or wiki) has been updated or is not required

[welcome]

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[pedropintosilva]

Hello @tobia and thanks for taking the time to setup Collabora Online and attempt to contribute! I think this one is best to be reviewed by @timar :)

[welcome]

Thanks a lot for your contribution, and congrats on your first pull request merged! Welcome aboard! 🎉🎉🎉

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