Closes #14173: Enable plugins to register columns on core tables (#14265)

* Closes #14173: Enable plugins to register columns on core tables

* Support translation for column name

* Document new registry store

docs/development/application-registry.md

@@ -53,6 +53,10 @@ This store maintains all registered items for plugins, such as navigation menus,
 
 A dictionary mapping each model (identified by its app and label) to its search index class, if one has been registered for it.
 
+### `tables`
+
+A dictionary mapping table classes to lists of extra columns that have been registered by plugins using the `register_table_column()` utility function. Each column is defined as a tuple of name and column instance.
+
 ### `views`
 
 A hierarchical mapping of registered views for each model. Mappings are added using the `register_model_view()` decorator, and URLs paths can be generated from these using `get_model_urls()`.

docs/plugins/development/tables.md

@@ -87,3 +87,28 @@ The table column classes listed below are supported for use in plugins. These cl
     options:
       members:
         - __init__
+
+## Extending Core Tables
+
+!!! info "This feature was introduced in NetBox v3.7."
+
+Plugins can register their own custom columns on core tables using the `register_table_column()` utility function. This allows a plugin to attach additional information, such as relationships to its own models, to built-in object lists.
+
+```python
+import django_tables2
+from django.utils.translation import gettext_lazy as _
+
+from dcim.tables import SiteTable
+from utilities.tables import register_table_column
+
+mycol = django_tables2.Column(
+    verbose_name=_('My Column'),
+    accessor=django_tables2.A('description')
+)
+
+register_table_column(mycol, 'foo', SiteTable)
+```
+
+You'll typically want to define an accessor identifying the desired model field or relationship when defining a custom column. See the [django-tables2 documentation](https://django-tables2.readthedocs.io/) for more information on creating custom columns.
+
+::: utilities.tables.register_table_column