Revert "dist/docker: Remove 'epel-release' from Docker image"
Revert "dist/docker: Remove 'epel-release' from Docker image"

This reverts commit ceb67e7728f80b6711bcc534292945e39bbbca52. The
"epel-release" package is needed to install the "supervisord"
package, which I somehow missed in testing...

Fixes #7851

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla