Support for custom domain url replacement

mobile/apps/photos/lib/services/collections_service.dart

@@ -755,10 +755,16 @@ class CollectionsService {
 
   String getPublicUrl(Collection c) {
     final PublicURL url = c.publicURLs.firstOrNull!;
+    Uri publicUrl = Uri.parse(url.url);
+    final String customDomain = flagService.customDomain;
+    if (customDomain.isNotEmpty) {
+      publicUrl =
+          publicUrl.replace(host: customDomain, scheme: "https", port: 443);
+    }
     final String collectionKey = Base58Encode(
       CollectionsService.instance.getCollectionKey(c.id),
     );
-    final String urlValue = "${url.url}#$collectionKey";
+    final String urlValue = "${publicUrl.toString()}#$collectionKey";
     return urlValue;
   }
 

mobile/apps/photos/plugins/ente_feature_flag/lib/src/service.dart

@@ -60,6 +60,8 @@ class FlagService {
 
   String get castUrl => flags.castUrl;
 
+  String get customDomain => flags.customDomain;
+
   bool hasSyncedAccountFlags() {
     return _prefs.containsKey("remote_flags");
   }