Discover EFS FileSystemId instead of specifying it in storage class

[avanish23]

What is this PR about? / Why do we need it?
This PR introduces the feature of discovering EFS FileSystemId instead of having to specify it in the SC parameters.
The way to use this feature is to create a storage class where the parameters have a new field fileSystemDiscovery.
Currently, it takes 2 fields creationToken and tags both being optional.
creationToken is a string that takes the creation token of the EFS to be discovered as input
tags is a map of strings
Sample Storage Class

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: efs-sc
provisioner: efs.csi.aws.com
parameters:
  provisioningMode: efs-ap
  directoryPerms: "700"
  gidRangeStart: "1000" # optional
  gidRangeEnd: "2000" # optional
  basePath: "/dynamic_provisioning" # optional
  subPathPattern: "${.PVC.namespace}/${.PVC.name}" # optional
  ensureUniqueDirectory: "true" # optional
  reuseAccessPoint: "false" # optional
  fileSystemDiscovery: |
    creationToken: aws-efs-for-discovery
    tags:
      env: prod
      owner: avanishpatil23@gmail.com

Note:

• use EFS Discovery with | as it is a multi-line string input
• fileSystemId will continue to be supported as a parameter
• if more than one EFS is discovered, the driver will throw an error; likewise, if no EFS is discovered
• the EFS discovery results are not cached

What testing is done?
Unit tests added and current unit tests pass

Closes #1052

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: avanish23
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[k8s-ci-robot]

Hi @avanish23. Thanks for your PR.

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