chore(portal): bump phoenix to 1.8 (#10510)

Bumps Phoenix to 1.8 and Phoenix LiveView to 1.1. As part of the bump a
number of issues had to be addressed. Comments inline provide more
context.

Supersedes #10475 
Supersedes #10448

elixir/apps/api/lib/api/controllers/fallback_controller.ex

@@ -1,5 +1,5 @@
 defmodule API.FallbackController do
-  use Phoenix.Controller
+  use API, :controller
 
   def call(conn, {:error, :not_found}) do
     conn

elixir/apps/api/mix.exs

@@ -43,7 +43,7 @@ defmodule API.MixProject do
       {:domain, in_umbrella: true},
 
       # Phoenix deps
-      {:phoenix, "~> 1.7.0"},
+      {:phoenix, "~> 1.8"},
       {:phoenix_ecto, "~> 4.4"},
       {:plug_cowboy, "~> 2.7"},