Rawkv gctask metrics (#12558)
Rawkv gctask metrics (#12558)

ref tikv/tikv#12557

Signed-off-by: ystaticy <y_static_y@sina.com>

Co-authored-by: iosmanthus <88650252a8c9994f143dbe614bec0323297ee204@pingcap.com>
Co-authored-by: Ti Chi Robot <040e6455cde1c91e876ec337e785ce913eacba35@tidb.io>
BusyJay/tikv,BusyJay/tikv,BusyJay/tikv,BusyJay/tikv