feat(api): split api into multiple apps (#1626)

Fixes #1622

- split the api into 4 apps: core, history, schedule, storage
- exploded the settings into testing/prod

api/libretime_api/storage/serializers/storage.py

@@ -0,0 +1,9 @@
+from rest_framework import serializers
+
+from ..models import MusicDir
+
+
+class MusicDirSerializer(serializers.HyperlinkedModelSerializer):
+    class Meta:
+        model = MusicDir
+        fields = "__all__"