Closes #11559: Implement config template rendering (#11769)

* WIP

* Add config_template field to Device

* Pre-fetch referenced templates

* Correct up_to_date callable

* Add config_template FK to Device

* Update & merge migrations

* Add config_template FK to Platform

* Add tagging support for ConfigTemplate

* Catch exceptions when rendering device templates in UI

* Refactor ConfigTemplate.render()

* Add support for returning plain text content

* Add ConfigTemplate model documentation

* Add feature documentation for config rendering

netbox/dcim/migrations/0170_configtemplate.py

@@ -0,0 +1,28 @@
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('extras', '0086_configtemplate'),
+        ('dcim', '0169_devicetype_default_platform'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='device',
+            name='config_template',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.PROTECT, related_name='devices', to='extras.configtemplate'),
+        ),
+        migrations.AddField(
+            model_name='devicerole',
+            name='config_template',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.PROTECT, related_name='device_roles', to='extras.configtemplate'),
+        ),
+        migrations.AddField(
+            model_name='platform',
+            name='config_template',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.PROTECT, related_name='platforms', to='extras.configtemplate'),
+        ),
+    ]