rpc: add max peer block height into /status rpc call (#6610)

use  `maxPeerBlockHeight` information to show the current network's best height.

Closes #3983
Relate to #3365

ref: the`highestBlock` in the response of `eth.isSyncing` call
https://web3js.readthedocs.io/en/v1.3.4/web3-eth.html#issyncing

rpc/openapi/openapi.yaml

@@ -484,7 +484,7 @@ paths:
       tags:
         - Info
       description: |
-        Get Tendermint status including node info, pubkey, latest block hash, app hash, block height and time.
+        Get Tendermint status including node info, pubkey, latest block hash, app hash, block height, current max peer height, and time.
       responses:
         "200":
           description: Status of the node
@@ -1324,6 +1324,9 @@ components:
         earliest_block_time:
           type: string
           example: "2019-08-01T11:52:22.818762194Z"
+        max_peer_block_height:
+          type: string
+          example: "1262196"
         catching_up:
           type: boolean
           example: false