Support debug and ctop commands in CLI

[aylei]

This PR add debug and ctop commands in the CLI, some examples:

$ tkc list -A
NAMESPACE            NAME                 PD    TIKV   TIDB   AGE
stability-cluster1   stability-cluster1   3/3   3/3    2/2    26h

$ tkc use -n=stability-cluster1 stability-cluster1
Tidb cluster switched to stability-cluster1/stability-cluster1

$ tkc get tikv
NAME                        READY   STATUS    MEMORY          CPU   RESTARTS   AGE   NODE
stability-cluster1-tikv-0   2/2     Running   2098Mi/4196Mi         0          26h   172.16.4.153
stability-cluster1-tikv-1   2/2     Running   2098Mi/4196Mi         0          26h   172.16.4.151
stability-cluster1-tikv-2   2/2     Running   2098Mi/4196Mi         0          26h   172.16.4.150

# Now, assume that stability-cluster1-tikv-0 is unhealthy, we can use `ctop` to view the real-time metrics
$ tkc ctop stability-cluster1-tikv-0
# Or see the node metrics of tikv-0
$ tkc ctop node/172.16.4.153

# If the problem still exists, we can debug the tikv instance
$ tkc debug stability-cluster1-tikv-0 

████████╗██╗██████╗ ██████╗      ██████╗████████╗██╗
╚══██╔══╝╚═╝██╔══██╗██╔══██╗    ██╔════╝╚══██╔══╝██║
   ██║   ██╗██║  ██║██████╔╝    ██║        ██║   ██║
   ██║   ██║██║  ██║██╔══██╗    ██║        ██║   ██║
   ██║   ██║██████╔╝██████╔╝    ╚██████╗   ██║   ███████╗
   ╚═╝   ╚═╝╚═════╝ ╚═════╝      ╚═════╝   ╚═╝   ╚══════╝

Welcome to tidb cluster control! (https://github.com/pingcap/tidb)

→ / ps -ef
PID   USER     TIME  COMMAND
    1 root      3:52 /tikv-server --pd=stability-cluster1-pd:2379 --advertise-a
  103 root      0:00 bash -l
  112 root      0:00 ps -ef

# we may chroot the tikv container's root filesystem
→ / chroot /proc/1/root

→ / ls
bin            home           mnt            sbin           tmp
dev            lib            proc           srv            usr
entrypoint.sh  lib64          root           sys            var
etc            media          run            tikv-server

I will open another PR to add more documents and tests.

Signed-off-by: Aylei rayingecho@gmail.com

[aylei]

/run-e2e-tests

[aylei]

@tennix @weekface @xiaojingchen PTAL again

[weekface]

This looks good to me.

[tennix]

LGTM