Added missing block header API (#630)

* header API frontend

* Block Header API endpoint added to Node.js backend

* updated package-lock.json

Co-authored-by: Rishabh <rishabh@Rajeshs-MacBook-Pro.local>

backend/src/api/bitcoin/bitcoin-api.ts

@@ -60,6 +60,10 @@ class BitcoinApi implements AbstractBitcoinApi {
     return this.bitcoindClient.getBlockHash(height);
   }
 
+  $getBlockHeader(hash: string): Promise<string> {
+    return this.bitcoindClient.getBlockHeader(hash,false);
+  }
+
   async $getBlock(hash: string): Promise<IEsploraApi.Block> {
     const foundBlock = blocks.getBlocks().find((block) => block.id === hash);
     if (foundBlock) {