feat: Add support for nulls_distinct in custom indexes

[sezaru]

This will add support for the nulls_distinct option for PG 15

More information in https://hexdocs.pm/ecto_sql/Ecto.Migration.html#index/3-the-nulls_distinct-option

Contributor checklist

• Bug fixes include regression tests
• Features include unit/acceptance tests

[sezaru]

Not sure why the mix test step fails, it runs just fine locally and the logs don't seem to give me a good reason

[jimsynz]

It's failing because there are migrations that should be generated.

[zachdaniel]

So the fact that this generates migrations for existing unchanged things is problematic. To address this, when loading a snapshot, we need to set the nulls_distinct? option to false if the option is not set.

[zachdaniel]

  defp load_custom_indexes(custom_indexes) do
    Enum.map(custom_indexes || [], fn custom_index ->
      custom_index
      |> Map.put_new(:fields, [])
      |> Map.put_new(:include, [])
      |> Map.put_new(:message, nil)
      |> Map.put_new(:nulls_distinct?, false) # something like this
    end)
  end