Standardize lag status response format

[yzang2019]

Describe your changes and provide context

This is to fix an issue reported: sei-protocol/sei-chain#1214

Testing performed to validate your change

Tested on local docker chain

root@6b45806c2360:/sei-protocol/sei-chain# curl localhost:26657/lag_status |jq
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    60  100    60    0     0   7340      0 --:--:-- --:--:-- --:--:-- 15000
{
  "current_height": "663",
  "max_peer_height": "991",
  "lag": "328"
}
root@6b45806c2360:/sei-protocol/sei-chain# curl localhost:26657/lag_status |jq
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    60  100    60    0     0   7483      0 --:--:-- --:--:-- --:--:-- 15000
{
  "current_height": "684",
  "max_peer_height": "991",
  "lag": "307"
}
root@6b45806c2360:/sei-protocol/sei-chain# curl localhost:26657/lag_status |jq
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    60  100    60    0     0   3548      0 --:--:-- --:--:-- --:--:--  6666
{
  "current_height": "694",
  "max_peer_height": "991",
  "lag": "297"
}