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

internal/blockchain/v0/reactor.go

@@ -589,3 +589,7 @@ FOR_LOOP:
 		}
 	}
 }
+
+func (r *Reactor) GetMaxPeerBlockHeight() int64 {
+	return r.pool.MaxPeerHeight()
+}

internal/blockchain/v2/reactor.go

@@ -590,3 +590,9 @@ func (r *BlockchainReactor) GetChannels() []*p2p.ChannelDescriptor {
 		},
 	}
 }
+
+func (r *BlockchainReactor) GetMaxPeerBlockHeight() int64 {
+	r.mtx.RLock()
+	defer r.mtx.RUnlock()
+	return r.maxPeerHeight
+}

internal/consensus/reactor.go

@@ -98,6 +98,14 @@ const (
 
 type ReactorOption func(*Reactor)
 
+// Temporary interface for switching to fast sync, we should get rid of v0.
+// See: https://github.com/tendermint/tendermint/issues/4595
+type FastSyncReactor interface {
+	SwitchToFastSync(sm.State) error
+
+	GetMaxPeerBlockHeight() int64
+}
+
 // Reactor defines a reactor for the consensus service.
 type Reactor struct {
 	service.BaseService