set other lxc templates to not default on change

proxmox/models.py

@@ -343,6 +343,11 @@ class LxcTemplate(ProxmoxAbstractModel, TaskAwareModelMixin):
     is_default_template = models.BooleanField(default=False,
                                               help_text='If true, this template will be used when creating new containers as default, or preselected')
 
+    def save(self, *args, **kwargs):
+        if self.is_default_template:
+            self.objects.filter(models.Q(is_default_template=True), ~models.Q(internal_id=self.pk)).update(is_default_template=False)
+        super().save(*args, **kwargs)
+
     def __str__(self):
         return self.volid.split('/')[-1]
 
@@ -352,3 +357,4 @@ class LxcTemplate(ProxmoxAbstractModel, TaskAwareModelMixin):
     @property
     def human_size(self):
         return human_size(self.size)
+