Immutability: also tag alpine version

[fenollp]

cc #289
In the continuation of the reproducible/immutability idea I suggest also marking Alpine's version in the tag.
e.g. turn erlang:22.3.4.10-alpine into erlang:22.3.4.10-alpine3.10
See e.g. https://hub.docker.com/_/python

Maybe also include the rebar3 version that's bundled with it as well: erlang:22.3.4.10-rebar3.13.2-alpine3.10