Missing Grafana URL output in json format

[onlyacat]

Bug Report

1. What did you do?

A cluster named test and there is a grafana instance in the cluster.

Then run tiup cluster display test and tiup cluster display test --format json

2. What did you expect to see?

Both can give the result of grafana URL.

3. What did you see instead?

The Grafana URL is missing in the result in json format.

4. What version of TiUP are you using (tiup --version)?

v1.10.2