Add info command

[vpnachev]

What would you like to be added:
gardenctl v1 has a info command that prints the number of active and hibernated shoots per seed cluster in the landscape, for example

$ gardenctl info
Garden: local
Seed               Total         Active        Hibernated
----               -----         ------        ----------
seed-1             8             3             5
seed-2             21            11            10
----               -----         ------        ----------
TOTAL              29            14            15
Unscheduled        0

Code ref: https://github.com/gardener/gardenctl/blob/v0.24.3/pkg/cmd/info.go
Eventually, the seed.status.(allocatable|capacity) fields can be also printed, ref: https://gardener.cloud/docs/gardener/api-reference/core/#core.gardener.cloud/v1beta1.SeedStatus

Why is this needed:
To get some insights about the size of the landscape and seed utilization.

[tedteng]

/assign will take a look