add tag and categories to video serializer

apps/core/serializers.py

 from rest_framework import serializers
 
-from .models import Video
+from .models import Video, Category, Tag, TagToObject
+
+
+class TagToObjectSerializer(serializers.ModelSerializer):
+    id = serializers.CharField(source='tag.id')
+    name = serializers.CharField(source='tag.name')
+
+    class Meta:
+        model = TagToObject
+        fields = ['id', 'name']
+
+
+class CategorySerializer(serializers.ModelSerializer):
+    class Meta:
+        model = Category
+        fields = ['id', 'name']
 
 
 class VideoSerializer(serializers.ModelSerializer):
+    categories = CategorySerializer(many=True)
+    tags = TagToObjectSerializer(many=True)
+
     class Meta:
         model = Video
         fields = [
@@ -12,4 +30,6 @@ class VideoSerializer(serializers.ModelSerializer):
             'description',
             's3_file',
             'thumbnail',
+            'categories',
+            'tags',
         ]