add dev email preview route

lib/cannery_web/controllers/email_controller.ex

@@ -0,0 +1,23 @@
+defmodule CanneryWeb.EmailController do
+  @moduledoc """
+  A dev controller used to develop on emails
+  """
+
+  use CanneryWeb, :controller
+  alias Cannery.Accounts.User
+
+  plug :put_layout, {CanneryWeb.LayoutView, :email}
+
+  @sample_assigns %{
+    email: %{subject: "Example subject"},
+    url: "https://cannery.bubbletea.dev/sample_url",
+    user: %User{email: "sample@email.com"}
+  }
+
+  @doc """
+  Debug route used to preview emails
+  """
+  def preview(conn, %{"id" => template}) do
+    render(conn, "#{template |> to_string()}.html", @sample_assigns)
+  end
+end