Url field fix (#3488)

* Updates for automated metadata extraction

* Update link field for StockItem model

- Increase max_length to 200 characters
- Custom migration
- Updates for InvenTreeUrlField model

* Adding unit tests

* Bug fix for metadata.py

InvenTree/stock/models.py

@@ -647,7 +647,7 @@ class StockItem(MetadataMixin, MPTTModel):
 
     link = InvenTreeURLField(
         verbose_name=_('External Link'),
-        max_length=125, blank=True,
+        blank=True, max_length=200,
         help_text=_("Link to external URL")
     )