AAE-30864 Refactored services to accept injected validators (#10660)

* [AAE-30864] refactored services to accept injected validators

* [AAE-30864] updated documentation, applied pr comments

docs/core/services/form.service.md

@@ -191,3 +191,32 @@ class MyComponent {
 -   `handleError(error: any):`[`Observable`](http://reactivex.io/documentation/observable.html)`<any>`  
     Reports an error message.  
     -   `error` - Data object with optional \`message\` and \`status\` fields for the error
+
+### Properties
+| Name | Type      | Description |
+| ---- | --------- | ----------- |
+| fieldValidators | FormFieldValidator[] | Array of Field Validators injected with token and then passed to FormModel |
+
+
+### Inject Preference service
+
+Token: [`FORM_SERVICE_FIELD_VALIDATORS_TOKEN`]
+A DI token that allows to inject additional form field validators.
+
+```ts
+import { NgModule } from '@angular/core';
+import { FORM_SERVICE_FIELD_VALIDATORS_TOKEN } from '@alfresco/adf-core';
+
+@NgModule({
+    imports: [
+        ...Import Required Modules
+    ],
+    providers: [
+        { 
+            provide: FORM_SERVICE_FIELD_VALIDATORS_TOKEN, 
+            useValue: [new AdditionalFormFieldValidator()]
+        }
+    ]
+})
+export class ExampleModule {}
+```