rpc: Enhance metadata of the dumptxoutset output

The following data is added:
- A newly introduced utxo set magic
- A version number
- The network magic
- The block height

test/functional/rpc_dumptxoutset.py

@@ -43,7 +43,7 @@ class DumptxoutsetTest(BitcoinTestFramework):
         # UTXO snapshot hash should be deterministic based on mocked time.
         assert_equal(
             sha256sum_file(str(expected_path)).hex(),
-            '3263fc0311ea46415b85513a59ad8fe67806b3cdce66147175ecb9da768d4a99')
+            '2f775f82811150d310527b5ff773f81fb0fb517e941c543c1f7c4d38fd2717b3')
 
         assert_equal(
             out['txoutset_hash'], 'a0b7baa3bf5ccbd3279728f230d7ca0c44a76e9923fca8f32dbfd08d65ea496a')