Feature: Implement custom fields for documents (#4502)

Adds custom fields of certain data types, attachable to documents and searchable

Co-Authored-By: Trenton H <797416+stumpylog@users.noreply.github.com>

src-ui/src/app/data/paperless-custom-field.ts

@@ -0,0 +1,48 @@
+import { ObjectWithId } from './object-with-id'
+
+export enum PaperlessCustomFieldDataType {
+  String = 'string',
+  Url = 'url',
+  Date = 'date',
+  Boolean = 'boolean',
+  Integer = 'integer',
+  Float = 'float',
+  Monetary = 'monetary',
+}
+
+export const DATA_TYPE_LABELS = [
+  {
+    id: PaperlessCustomFieldDataType.Boolean,
+    name: $localize`Boolean`,
+  },
+  {
+    id: PaperlessCustomFieldDataType.Date,
+    name: $localize`Date`,
+  },
+  {
+    id: PaperlessCustomFieldDataType.Integer,
+    name: $localize`Integer`,
+  },
+  {
+    id: PaperlessCustomFieldDataType.Float,
+    name: $localize`Number`,
+  },
+  {
+    id: PaperlessCustomFieldDataType.Monetary,
+    name: $localize`Monetary`,
+  },
+  {
+    id: PaperlessCustomFieldDataType.String,
+    name: $localize`Text`,
+  },
+  {
+    id: PaperlessCustomFieldDataType.Url,
+    name: $localize`Url`,
+  },
+]
+
+export interface PaperlessCustomField extends ObjectWithId {
+  data_type: PaperlessCustomFieldDataType
+  name: string
+  created?: Date
+}