[Feature] Expose the metrics fro multinode ETCD

[abdasgupta]

Feature (What you would like to be added):
Expose the metrics that is listed in the running doc
Motivation (Why is this needed?):
We need to expose the metrics in the codebase so that prometheus can collect the metrics and convert them into meaningful representation for the support.
Approach/Hint to the implement solution (optional):

[ishan16696]

Mentioning the metric which I found while doing feature of single member restoration in multi-node etcd:
Add metrics:

• Whether the single node restoration in multi-node etcd is successful or not.
• How much time it will while the restoration of single member in multi-node etcd.
  like in single node cluster's restoration (refer here).

[ishan16696]

closing this issue as this has been implemented with PR: gardener/etcd-backup-restore#522
/close