Adding a Kanister function to create CSI VolumeSnapshot

[shlokc9]

Change Overview

This PR consist of a new Kanister function to create CSI VolumeSnapshot along with it's documentation

Pull request type

Please check the type of change your PR introduces:

• 🚧 Work in Progress
• 🌈 Refactoring (no functional changes, no api changes)
• 🐹 Trivial/Minor
• 🐛 Bugfix
• 🌻 Feature
• 🗺️ Documentation
• 🤖 Test

Issues

• Kanister Functions for creating CSI snapshots #1126

Test Plan

• 💪 Manual
• ⚡ Unit test
• 💚 E2E

[bathina2]

Looks good. Can you add some unit tests? I'll let someone else approve.

[viveksinghggits]

LGTM

[PrasadG193]

LGTM

[shlokc9]

backup action that runs create phase in BP:

actions:
  backup:
    outputArtifacts:
      snapshotInfo:
        keyValue:
          name: "{{ .Phases.createCSISnapshot.Output.name }}"
          pvc: "{{ .Phases.createCSISnapshot.Output.pvc }}"
          namespace: "{{ .Phases.createCSISnapshot.Output.namespace }}"
          restoreSize: "{{ .Phases.createCSISnapshot.Output.restoreSize }}"
          snapshotContent: "{{ .Phases.createCSISnapshot.Output.snapshotContent }}"
    phases:
    - func: CreateCSISnapshot
      name: createCSISnapshot
      args:
        pvc: "{{ .PVC.Name }}"
        namespace: "{{ .PVC.Namespace }}"
        snapshotClass: do-block-storage