Add support for own Smileys (lib/images/smileys/local)

[Qube2org]

Hi,

Thanks for providing Docker support for the great DokuWiki!

I am currently trying to migrate an existing DokuWiki instance from a local server to the Docker image. However, I encountered a problem: the site makes extensive use of custom smileys, which are not working in the Docker container because there is no access to the directory lib/images/smileys/local.

It would be very helpful if the Docker setup could support custom smileys by relocating this directory into the storage volume and linking it accordingly inside the container.

Thank you for considering this feature request!

[Qube2org]

Found this is similar to Pull request #16