Makes outbox an optional field on the user table

bookwyrm/migrations/0061_auto_20210402_1435.py

@@ -0,0 +1,24 @@
+# Generated by Django 3.1.6 on 2021-04-02 14:35
+
+import bookwyrm.models.fields
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookwyrm", "0060_siteinvite_invitees"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="user",
+            name="outbox",
+            field=bookwyrm.models.fields.RemoteIdField(
+                max_length=255,
+                null=True,
+                unique=True,
+                validators=[bookwyrm.models.fields.validate_remote_id],
+            ),
+        ),
+    ]