Annotate postgres enums

[andys]

Currently a Postgres enum column shows, eg:

#  state                    :enum             default("creating"), not null

The actual schema contains:

 t.enum "state", default: "creating", null: false, enum_type: "states"

create_enum :states, [
    "creating",
    "deploying",
    "completed",
    "failed",
    "superseded",
  ], force: :cascade

Which is more useful information for the developer.

[drwl]

Hi @andys I believe this is known. I don't have time to take this on, but if you would like to submit a PR I can review it.

#176 gave an ideal example -- thoughts on it?