[Plugin] Allow custom plugins for running validation routines (#3776)

* Adds new plugin mixin for performing custom validation steps

* Adds simple test plugin for custom validation

* Run part name and IPN validators checks through loaded plugins

* Expose more validation functions to plugins:

- SalesOrder reference
- PurchaseOrder reference
- BuildOrder reference

* Remove custom validation of reference fields

- For now, this is too complex to consider given the current incrementing-reference implementation
- Might revisit this at a later stage.

* Custom validation of serial numbers:

- Replace "checkIfSerialNumberExists" method with "validate_serial_number"
- Pass serial number through to custom plugins
- General code / docstring improvements

* Update unit tests

* Update InvenTree/stock/tests.py

Co-authored-by: Matthias Mair <code@mjmair.com>

* Adds global setting to specify whether serial numbers must be unique globally

- Default is false to preserve behaviour

* Improved error message when attempting to create stock item with invalid serial numbers

* Add more detail to existing serial error message

* Add unit testing for serial number uniqueness

* Allow plugins to convert a serial number to an integer (for optimized sorting)

* Add placeholder plugin methods for incrementing and decrementing serial numbers

* Typo fix

* Add improved method for determining the "latest" serial number

* Remove calls to getLatestSerialNumber

* Update validate_serial_number method

- Add option to disable checking for duplicates
- Don't pass optional StockItem through to plugins

* Refactor serial number extraction methods

- Expose the "incrementing" portion to external plugins

* Bug fixes

* Update unit tests

* Fix for get_latest_serial_number

* Ensure custom serial integer values are clipped

* Adds a plugin for validating and generating hexadecimal serial numbers

* Update unit tests

* Add stub methods for batch code functionality

* remove "hex serials" plugin

- Was simply breaking unit tests

* Allow custom plugins to generate and validate batch codes

- Perform batch code validation when StockItem is saved
- Improve display of error message in modal forms

* Fix unit tests for stock app

* Log message if plugin has a duplicate slug

* Unit test fix

Co-authored-by: Matthias Mair <code@mjmair.com>

InvenTree/common/models.py

@@ -1139,6 +1139,13 @@ class InvenTreeSetting(BaseInvenTreeSetting):
             'validator': bool,
         },
 
+        'SERIAL_NUMBER_GLOBALLY_UNIQUE': {
+            'name': _('Globally Unique Serials'),
+            'description': _('Serial numbers for stock items must be globally unique'),
+            'default': False,
+            'validator': bool,
+        },
+
         'STOCK_BATCH_CODE_TEMPLATE': {
             'name': _('Batch Code Template'),
             'description': _('Template for generating default batch codes for stock items'),