♻️ Add HTTP interface

lib/http.ex

@@ -0,0 +1,8 @@
+defmodule Mater.HTTP do
+  @moduledoc """
+  HTTP Client interface to communicate with GraphQL APIs.
+  """
+
+  def call(),
+    do: :todo
+end

lib/http/interface.ex

@@ -0,0 +1,14 @@
+defmodule Mater.HTTP.Interface do
+  @moduledoc """
+  This module represents the interface functions that
+  should be implemented when using HTTP Clients to
+  access a GraphQL API resource.
+  """
+
+  @type endpoint :: String.t()
+  @type body :: %{query: String.t(), variables: String.t()}
+  @type opts :: Keyword.t()
+  @type response :: {:ok, map()} | {:error, map()}
+
+  @callback call(endpoint, body, opts) :: response
+end