Allow custom extensions to use options

[greg-rychlewski]

Currently the extensions users create themselves cannot access the options passed to the type module. A few of the options, like :null and :decode_binary seem like they should be passed to them. For example, we previously asked users to define their own ltree and lquery extensions and our own implementations are using the :decode_binary option. Also, our own documented example of a custom extension is passed the opts https://hexdocs.pm/postgrex/Postgrex.Extension.html

[greg-rychlewski]

I had a misunderstanding. We ask the user to pass a tuple if they want opts:

Postgrex.Types.define(MyApp.Types, [{MyApp.LTree, [decode_copy: :copy]}])

Closing this