Use musicbrainz_id as a key for embedded artists

lib/music_library/records/record.ex

@@ -22,11 +22,10 @@ defmodule MusicLibrary.Records.Record do
     field :release_ids, {:array, :string}, default: []
     field :included_release_group_ids, {:array, :string}, default: []
 
-    embeds_many :artists, Artist do
+    embeds_many :artists, Artist, primary_key: {:musicbrainz_id, :binary_id, autogenerate: false} do
       field :name, :string
       field :sort_name, :string
       field :disambiguation, :string
-      field :musicbrainz_id, Ecto.UUID
     end
 
     timestamps(type: :utc_datetime)

test/music_library_web/live/collection_live/index_test.exs

@@ -343,7 +343,6 @@ defmodule MusicLibraryWeb.CollectionLive.IndexTest do
       [marillion] = record.artists
 
       assert %MusicLibrary.Records.Record.Artist{
-               id: _,
                name: "Marillion",
                sort_name: "Marillion",
                disambiguation: "British progressive rock band",