models: Add UserProfile field for custom email notifs batching periods.

The default is 2 minutes (120 seconds), which was the hardcoded value
earlier.

zerver/migrations/0334_email_notifications_batching_period.py

@@ -0,0 +1,23 @@
+# Generated by Django 3.2.5 on 2021-07-19 11:00
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("zerver", "0333_alter_realm_org_type"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="realmuserdefault",
+            name="email_notifications_batching_period_seconds",
+            field=models.IntegerField(default=120),
+        ),
+        migrations.AddField(
+            model_name="userprofile",
+            name="email_notifications_batching_period_seconds",
+            field=models.IntegerField(default=120),
+        ),
+    ]

zerver/models.py

@@ -1299,6 +1299,8 @@ class UserBaseSettings(models.Model):
 
     ### Notifications settings. ###
 
+    email_notifications_batching_period_seconds: int = models.IntegerField(default=120)
+
     # Stream notifications.
     enable_stream_desktop_notifications: bool = models.BooleanField(default=False)
     enable_stream_email_notifications: bool = models.BooleanField(default=False)
@@ -1350,6 +1352,7 @@ class UserBaseSettings(models.Model):
         enable_digest_emails=bool,
         enable_login_emails=bool,
         enable_marketing_emails=bool,
+        email_notifications_batching_period_seconds=int,
         enable_offline_email_notifications=bool,
         enable_offline_push_notifications=bool,
         enable_online_push_notifications=bool,