feat: add join confirmation and mail templating

test/membership/join_request_submit_email_test.exs

@@ -26,6 +26,7 @@ defmodule Mv.Membership.JoinRequestSubmitEmailTest do
 
       assert_email_sent(fn email_sent ->
         to_addresses = Enum.map(email_sent.to, &elem(&1, 1))
+
         to_string(email) in to_addresses and
           (email_sent.html_body =~ "/confirm_join/" or email_sent.text_body =~ "/confirm_join/")
       end)

test/mv_web/controllers/join_confirm_controller_test.exs

@@ -87,7 +87,6 @@ defmodule MvWeb.JoinConfirmControllerTest do
       conn = get(conn, "/confirm_join/public-test-token")
 
       assert conn.status == 200
-      refute redirected_to(conn) =~ "/sign-in"
     end
   end
 end