Fix LiveView warning when uploading device certificates, rehydrate state properly (#2280)

`Phoenix.LiveView. consume_uploaded_entry/3` expects the function passed
to return `{:ok, _return}` or `{:postpone, _return}`. We were returning
a socket, causing a warning in the logs:

```
iex(21)> warning: consuming uploads requires a return signature matching:

    {:ok, value} | {:postpone, value}

got:

    #Phoenix.LiveView.Socket<...>

  (phoenix_live_view 1.1.3) lib/phoenix_live_view/upload_channel.ex:33: Phoenix.LiveView.UploadChannel.consume/3
  (elixir 1.18.3) lib/enum.ex:1714: Enum."-map/2-lists^map/1-1-"/2
  (phoenix_live_view 1.1.3) lib/phoenix_live_view/upload.ex:264: Phoenix.LiveView.Upload.consume_uploaded_entry/3
  (nerves_hub 2.0.0+afbd8e1f) lib/nerves_hub_web/components/device_page/settings_tab.ex:424: NervesHubWeb.Components.DevicePage.SettingsTab.handle_progress/3
  (phoenix_live_view 1.1.3) lib/phoenix_live_view/channel.ex:181: anonymous fn/4 in Phoenix.LiveView.Channel.handle_info/2
  (phoenix_live_view 1.1.3) lib/phoenix_live_view/channel.ex:1525: Phoenix.LiveView.Channel.write_socket/4
  (phoenix_live_view 1.1.3) lib/phoenix_live_view/channel.ex:174: Phoenix.LiveView.Channel.handle_info/2
  (stdlib 6.2.2) gen_server.erl:2345: :gen_server.try_handle_info/3
  (stdlib 6.2.2) gen_server.erl:2433: :gen_server.handle_msg/6
  (stdlib 6.2.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3
```

I also fixed an issue when uploading a device certificate. We were
previously using `update_in/2`, but on an unloaded Ecto association.
This was copied over from the old UI, but this code now sits in a
component, and we don't preload device certificates in the parent
LiveView. Fixing this uncovered another bug if you deleted the device's
last cert and then uploaded a new one. `Repo.preload/3` won't preload on
a loaded empty association, so `force: true` is needed.

Author: nshoes

lib/nerves_hub_web.ex

@@ -356,6 +356,8 @@ defmodule NervesHubWeb do
 
       defoverridable tab_params: 3, cleanup: 0
 
+      def ok(socket), do: {:ok, socket}
+
       def halt(socket), do: {:halt, socket}
 
       def cont(socket), do: {:cont, socket}

lib/nerves_hub_web/components/device_page/settings_tab.ex

@@ -22,7 +22,7 @@ defmodule NervesHubWeb.Components.DevicePage.SettingsTab do
   end
 
   def render(assigns) do
-    device = Repo.preload(assigns.device, :device_certificates)
+    device = Repo.preload(assigns.device, :device_certificates, force: true)
 
     changeset = Ecto.Changeset.change(assigns.device)
 
@@ -431,25 +431,30 @@ defmodule NervesHubWeb.Components.DevicePage.SettingsTab do
   defp import_cert(%{assigns: %{device: device}} = socket, path) do
     with {:ok, pem_or_der} <- File.read(path),
          {:ok, otp_cert} <- Certificate.from_pem_or_der(pem_or_der),
-         {:ok, db_cert} <- Devices.create_device_certificate(device, otp_cert) do
-      updated = update_in(device.device_certificates, &[db_cert | &1])
+         {:ok, _db_cert} <- Devices.create_device_certificate(device, otp_cert) do
+      updated = Repo.preload(device, :device_certificates)
 
       assign(socket, :device, updated)
       |> put_flash(:info, "Certificate Upload Successful")
+      |> ok()
     else
       {:error, :malformed} ->
-        put_flash(socket, :error, "Incorrect filetype or malformed certificate")
+        {:ok, put_flash(socket, :error, "Incorrect filetype or malformed certificate")}
 
       {:error, %Ecto.Changeset{errors: errors}} ->
         formatted =
           Enum.map_join(errors, "\n", fn {field, {msg, _}} ->
             ["* ", to_string(field), " ", msg]
           end)
 
-        put_flash(socket, :error, IO.iodata_to_binary(["Failed to save:\n", formatted]))
+        socket
+        |> put_flash(:error, IO.iodata_to_binary(["Failed to save:\n", formatted]))
+        |> ok()
 
       err ->
-        put_flash(socket, :error, "Unknown file error - #{inspect(err)}")
+        socket
+        |> put_flash(:error, "Unknown file error - #{inspect(err)}")
+        |> ok()
     end
   end