Add tzdata package inside docker image

*This issue was originally created by [**@magostinelli**](https://github.com/magostinelli) at .*

Timezone in docker setup is not working, the chat time is wrong.

It's possible to add the tzdata package in the official docker image? (matrixdotorg/dendrite-monolith:main):
apk add tzdata

If I manually install the package everything works as expected.

Regards.

Inspect the Docker image definition for matrixdotorg/dendrite-monolith:main and reproduce the timezone behavior before installing tzdata manually. Done means the official image includes tzdata and chat times are correct without a manual package installation.

Written by the indexing model from the issue text.