Add last valid block height to rpc Fees (#17506)

* Add last_valid_block_height to fees rpc

* Add getBlockHeight rpc

* Update docs

client/src/rpc_request.rs

@@ -12,6 +12,7 @@ pub enum RpcRequest {
     GetAccountInfo,
     GetBalance,
     GetBlock,
+    GetBlockHeight,
     GetBlockProduction,
     GetBlocks,
     GetBlocksWithLimit,
@@ -95,6 +96,7 @@ impl fmt::Display for RpcRequest {
             RpcRequest::GetAccountInfo => "getAccountInfo",
             RpcRequest::GetBalance => "getBalance",
             RpcRequest::GetBlock => "getBlock",
+            RpcRequest::GetBlockHeight => "getBlockHeight",
             RpcRequest::GetBlockProduction => "getBlockProduction",
             RpcRequest::GetBlocks => "getBlocks",
             RpcRequest::GetBlocksWithLimit => "getBlocksWithLimit",