Add Metadata to more models (#4898)

* Update models: add MetadataMixin

* Fix name of model in Metadata API definition

* Add API endpoints

* Update API version

* Fix syntax

* Add API endpoint for RO, RO line, RO line extra item

* Add Metadata to Contacts

* Fix link in API version

* Fix name of model

* Fix error?

* Fix error?

* Fix all errors, hopefully..

* Add tests for order, line, extraline metadata

Extend for PO, SO

* Add tests for metadata for Company-related models

* Fix spelling

* Consolidate metadata test for all part models into one test

* Add test for all Stock metadata

* Update stock test_api

* Add all metadata tests for orders

* Fix various errors in tests

* Fix model name

* Add migration files

* Update tests for metadata

* Resolve conflict around API version number

* Rename migration file

* Rename migration file

* Will Contact edit endpoint work better?

* Revert changes in URL definitions

* Remove test, duplicate

* Fix tests with fixed PK, not from fixtures, to use a dynamic PK

* Fix migration overlap

InvenTree/company/migrations/0062_contact_metadata.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.2.19 on 2023-05-25 16:06
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('company', '0061_remove_supplierpart_pack_size'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='contact',
+            name='metadata',
+            field=models.JSONField(blank=True, help_text='JSON metadata field, for use by external plugins', null=True, verbose_name='Plugin Metadata'),
+        ),
+    ]