fix(backend): Accept arrays in ActivityPub `icon` and `image` properties (#14825)

This is allowed according to the Activity vocabulary: https://www.w3.org/TR/activitystreams-vocabulary/#dfn-icon
The issue is noticeable in combination with Bridgy Fed: https://github.com/snarfed/bridgy-fed/issues/1408

packages/backend/src/core/activitypub/models/ApPersonService.ts

@@ -232,6 +232,12 @@ export class ApPersonService implements OnModuleInit {
 		if (user == null) throw new Error('failed to create user: user is null');
 
 		const [avatar, banner] = await Promise.all([icon, image].map(img => {
+			// icon and image may be arrays
+			// see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-icon
+			if (Array.isArray(img)) {
+				img = img.find(item => item && item.url) ?? null;
+			}
+			
 			// if we have an explicitly missing image, return an
 			// explicitly-null set of values
 			if ((img == null) || (typeof img === 'object' && img.url == null)) {