[incubator/monochart] Add support for volume snapshots

[osterman]

what

• Be able to restore an EBS Snapshot ID to EBS Volume used by a StatefulSet
• I think we need to add support for some CRDs

why

• To support snapshotting

references

• https://blog.jetstack.io/blog/volume-snapshotting/

[alebabai]

@osterman about snapshots.
Are you really sure to do in monochart scope?
Snapshot controller & provisioner should have a new deployment - maybe it's better to move it to he new chart and use use it here for example.
https://github.com/kubernetes-incubator/external-storage/tree/master/snapshot/deploy/kubernetes/aws
But i can't clearly imagine how to use snapshots using monochart workflow. It's more about manual steps.

[alebabai]

@osterman
So after some re-search in this area I made the following conclusions:

• kubernetes 1.12 has snapshots support - https://kubernetes.io/blog/2018/10/09/introducing-volume-snapshot-alpha-for-kubernetes/
• https://github.com/kubernetes-incubator/external-storage/tree/master/snapshot it seems like working solution for that, but it a really tricky to use it with StatefulSet because SS uses dynamic volume provisioning for each replica, but snapshot approach relies on static volume provisioning.

[alebabai]

@osterman hereis good article about how to restore volume from existing EBS Snapshot and attach it to SS, but there is a problem that i already described - it works only for replicaCount = 1
https://medium.com/@joatmon08/kubernetes-statefulset-recovery-from-aws-snapshots-8a6159cda6f1