models: Migrate ids of UserActivity and UserActivityInterval to bigint.

These models have no external references, and are among the larger
tables.  Migrate them to bigints, starting with `useractivityinterval`
which is less likely to be being touched.

zerver/migrations/0530_alter_useractivity_id_alter_useractivityinterval_id.py

@@ -0,0 +1,26 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("zerver", "0529_fts_bigint_id"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="useractivityinterval",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="useractivity",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+    ]

zerver/models/user_activity.py

@@ -19,6 +19,9 @@ class UserActivity(models.Model):
     and database migration purposes.
     """
 
+    id = models.BigAutoField(
+        auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+    )
     user_profile = models.ForeignKey(UserProfile, on_delete=CASCADE)
     client = models.ForeignKey(Client, on_delete=CASCADE)
     query = models.CharField(max_length=50, db_index=True)
@@ -33,6 +36,9 @@ class UserActivity(models.Model):
 class UserActivityInterval(models.Model):
     MIN_INTERVAL_LENGTH = timedelta(minutes=15)
 
+    id = models.BigAutoField(
+        auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+    )
     user_profile = models.ForeignKey(UserProfile, on_delete=CASCADE)
     start = models.DateTimeField("start time", db_index=True)
     end = models.DateTimeField("end time", db_index=True)