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/services/rest/custom-fields.service.spec.ts

@@ -0,0 +1,14 @@
+import { HttpTestingController } from '@angular/common/http/testing'
+import { Subscription } from 'rxjs'
+import { TestBed } from '@angular/core/testing'
+import { environment } from 'src/environments/environment'
+import { commonAbstractPaperlessServiceTests } from './abstract-paperless-service.spec'
+import { CustomFieldsService } from './custom-fields.service'
+
+let httpTestingController: HttpTestingController
+let service: CustomFieldsService
+let subscription: Subscription
+const endpoint = 'custom_fields'
+
+// run common tests
+commonAbstractPaperlessServiceTests(endpoint, CustomFieldsService)

src-ui/src/app/services/rest/custom-fields.service.ts

@@ -0,0 +1,15 @@
+import { Injectable } from '@angular/core'
+import { HttpClient, HttpParams } from '@angular/common/http'
+import { AbstractPaperlessService } from './abstract-paperless-service'
+import { Observable } from 'rxjs'
+import { PaperlessCustomField } from 'src/app/data/paperless-custom-field'
+import { PaperlessCustomFieldInstance } from 'src/app/data/paperless-custom-field-instance'
+
+@Injectable({
+  providedIn: 'root',
+})
+export class CustomFieldsService extends AbstractPaperlessService<PaperlessCustomField> {
+  constructor(http: HttpClient) {
+    super(http, 'custom_fields')
+  }
+}