Updates the mail db model to use the built-in enum capabilities and runs the migrations

src/paperless_mail/migrations/0009_alter_mailrule_action_alter_mailrule_folder.py

@@ -0,0 +1,37 @@
+# Generated by Django 4.0.3 on 2022-03-28 17:40
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("paperless_mail", "0008_auto_20210516_0940"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="mailrule",
+            name="action",
+            field=models.PositiveIntegerField(
+                choices=[
+                    (1, "Mark as read, don't process read mails"),
+                    (2, "Flag the mail, don't process flagged mails"),
+                    (3, "Move to specified folder"),
+                    (4, "Delete"),
+                ],
+                default=3,
+                verbose_name="action",
+            ),
+        ),
+        migrations.AlterField(
+            model_name="mailrule",
+            name="folder",
+            field=models.CharField(
+                default="INBOX",
+                help_text="Subfolders must be separated by a delimiter, often a dot ('.') or slash ('/'), but it varies by mail server.",
+                max_length=256,
+                verbose_name="folder",
+            ),
+        ),
+    ]