Fix permissions in Docker image

[kdeininger]

Running a container using the current Docker image results in an error:

docker: Error response from daemon: OCI runtime create failed: container_linux.go:349: starting container process caused "exec: \"/usr/local/bin/uid_entrypoint.sh\": permission denied": unknown.

This error gets fixed with this PR by

• copying the uid_entrypoint.sh before switching to user 1001 to get the specified owner applied and
• making uid_entrypoint.sh executable.