Add subsquare external links for Acala and Bifrost (#6825)

* Add Acala and Bifrost to Subsquare supported chains

* Solve the erroneous import in singular.ts

packages/apps-config/src/links/singular.ts

@@ -1,7 +1,7 @@
 // Copyright 2017-2022 @polkadot/apps-config authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
-import type BN from 'bn.js';
+import type { BN } from '@polkadot/util';
 
 import { externalLogos } from '../ui/logos';
 

packages/apps-config/src/links/subsquare.ts

@@ -7,6 +7,8 @@ import { externalLogos } from '../ui/logos';
 
 export default {
   chains: {
+    Acala: 'acala',
+    Bifrost: 'bifrost',
     Karura: 'karura',
     Khala: 'khala'
   },