push deprecated containers when rotating out distributions

[avsm]

As people use (e.g.) ocurrent/opam:alpine-3.11-ocaml-4.09, it will steadily get more out of date and have security issues in the base distribution.

ocaml-dockerfile provides a Dockerfile_opam.deprecated container that simply outputs an error message when invoked. After a few months of deprecation, we should push these to replace the older tags.

As part of this, we should check that we have aliases (e.g., does alpine-4.09 exist? That would be a good alias to say "give me OCaml 4.09 on Alpine without the latest Alpine release").