corporate: Add required_plan_tier field to Customer model.

This will be used to set a required plan tier value to be used with
the default discount that is set on the Customer object or with a
fixed price set on a CustomerPlan object.

corporate/migrations/0034_customer_discount_required_tier.py

@@ -0,0 +1,17 @@
+# Generated by Django 4.2.8 on 2024-01-09 14:28
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("corporate", "0033_customerplan_invoice_overdue_email_sent"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="customer",
+            name="required_plan_tier",
+            field=models.SmallIntegerField(null=True),
+        ),
+    ]

corporate/models.py

@@ -29,6 +29,9 @@ class Customer(models.Model):
     # A percentage, like 85.
     default_discount = models.DecimalField(decimal_places=4, max_digits=7, null=True)
     minimum_licenses = models.PositiveIntegerField(null=True)
+    # Used for limiting a default_discount or a fixed_price
+    # to be used only for a particular CustomerPlan tier.
+    required_plan_tier = models.SmallIntegerField(null=True)
     # Some non-profit organizations on manual license management pay
     # only for their paid employees.  We don't prevent these
     # organizations from adding more users than the number of licenses