Add more legend for cluster metrics (#3537)
Add more legend for cluster metrics (#3537)

* fix

Signed-off-by: lhy1024 <admin@liudos.us>

* fix label

Signed-off-by: lhy1024 <admin@liudos.us>

Co-authored-by: 混沌DM <86b53920241ddf9ae27a84e4620fda3038083636@gmail.com>
Co-authored-by: Ti Chi Robot <72214b26dd6f24c8c411751e1f8e05856122286e@users.noreply.github.com>
pingcap/pd,pingcap/pd