dockers: change to create symlink instead of copy

[bradymiller]

change to create symlink instead of copy

In Dockerfile of 7.0.3 and 7.0.4:
https://github.com/openemr/openemr-devops/blob/master/docker/openemr/7.0.3/Dockerfile#L19
https://github.com/openemr/openemr-devops/blob/master/docker/openemr/7.0.4/Dockerfile#L19