Allow docker to take multiple configuration files (e.g. for worker mode)

[JuniorJPDJ]

If I understood docs correctly - this feature is already working outside of docker and worker docs are written like it were available in every supported scenario - also in docker.
I managed to run workers in docker (after few days of fight with docs not being docker-ready - #8053).
Now I'm concatenating configs outside of docker, which is far from ideal solution, I need to remember to refresh configs after change in homeserver.yaml and in worker config itself.

[clokep]

I suspect what would be nice is if you can give the docker container multiple configuration files, which is what the worker docs assume is possible?

[JuniorJPDJ]

It's better approach of what I was thinking about, thank you for specification :)

[ptman]

Would that help help with #6662 as well?

[JuniorJPDJ]

@ptman It could ;D

[richvdh]

It sounds like this might just be a duplicate of #6662?

[clokep]

Sounds like a duplicate, yep!