Add 'Tag' management (#4367)

* 'Tag' management
Fixes #83

* Add for ManufacturerPart, SupplierPart

* Add tags for StockLocation, StockItem

* fix serializer definition

* add migrations

* update pre-commit

* bump dependencies

* revert updates

* set version for bugbear

* remove bugbear

* readd bugbear remove isort

* and remove bugbear again

* remove bugbear

* make tag fields not required

* add ruleset

* Merge migrations

* fix migrations

* add unittest for detail

* test tag add

* order api

* reduce database access

* add tag modification test

* use overriden serializer to ensuer the manager is always available

* fix typo

* fix serializer

* increae query thershold by 1

* move tag serializer

* fix migrations

* content_types are changing between tests - removing them

* remove unneeded fixture

* Add basic docs

* bump API version

* add api access to the docs

* add python code

* Add tags to search and filters for all models

docs/docs/extend/plugins/tags.md

@@ -0,0 +1,61 @@
+---
+title: Item Tags
+---
+
+## Tags
+
+Several models in InvenTree can be tagged with arbitrary tags. Tags are useful for grouping items together. This can be used to mark items with a plugin or to group items together for a particular theme. Tags are meant to be used by programms and are not visible to the end user.
+Tags are shared between all models that can be tagged.
+
+The following models can be tagged:
+- [Parts](../../part/part.md) and [Supplier Parts](../../order/company#supplier-parts)/[Manufacturer Part](../../order/company#manufacturer-parts)
+- [Stock Items](../../stock/stock.md#stock-item) / [Stock Location](../../stock/stock.md#stock-location)
+
+
+## Accessing Tags
+
+### Plugin Access
+
+The `tags` field can be accessed and updated directly from custom plugin code, as follows:
+
+```python
+from part.models import Part
+
+# Show tags for a particular Part instance
+part = Part.objects.get(pk=100)
+print(part.tags)
+
+> {['Tag1', 'Another Tag']}
+
+# Tags can also be accessed via tags.all()
+print(part.tags.all())
+
+> {['Tag1', 'Another Tag']}
+
+# Add tag
+part.tags.add('Tag 2')
+print(part.tags)
+
+> {['Tag1', 'Tag 2', 'Another Tag']}
+
+# Remove tag
+part.tags.remove('Tag1')
+print(part.tags)
+
+> {['Tag 2', 'Another Tag']}
+
+# Filter by tags
+Part.objects.filter(tags__name__in=["Tag1", "Tag 2"]).distinct()
+```
+
+### API Access
+
+For models which provide tags, access is also provided via the API. The tags are exposed via the detail endpoint for the models starting from version 111.
+
+Tags can be cached via PATCH or POST requests. The tags are provided as a json formatted list of strings. The tags are note case sensitive and must be unique across the instance - else the exsisting tag gets assigned. The tags are not sorted and the order is not guaranteed.
+
+```json
+{
+    "tags": '["foo", "bar"]'
+}
+```

docs/mkdocs.yml

@@ -166,6 +166,7 @@ nav:
       - Installation: extend/plugins/install.md
       - Developing a Plugin: extend/how_to_plugin.md
       - Model Meatadata: extend/plugins/metadata.md
+      - Tags: extend/plugins/tags.md
     - Plugin Mixins:
       - Action Mixin: extend/plugins/action.md
       - API Mixin: extend/plugins/api.md