Generate fewer add_status_tasks

Previously, every time a status was saved, a task would start to add it
to people's timelines. This meant there were a ton of duplicate tasks
that were potentially heavy to run. Now, the Status model has a "ready"
field which indicates that it's worth updating the timelines. It
defaults to True, which prevents statuses from accidentally not being
added due to ready state.

The ready state is explicitly set to false in the view, which is the
source of most of the noise for that task.

bookwyrm/migrations/0164_status_ready.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.2.16 on 2022-11-15 21:40
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookwyrm", "0163_merge_0160_auto_20221101_2251_0162_importjob_task_id"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="status",
+            name="ready",
+            field=models.BooleanField(default=True),
+        ),
+    ]