Extract ApiKeyCount from state.

public/app/features/api-keys/state/selectors.ts

@@ -1,5 +1,7 @@
 import { ApiKeysState } from 'app/types';
 
+export const getApiKeysCount = (state: ApiKeysState) => state.keys.length;
+
 export const getApiKeys = (state: ApiKeysState) => {
   const regex = RegExp(state.searchQuery, 'i');