Add support for backup PVC configuration

[shubham-pampattiwar]

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Please add a summary of your change

Implementation for Design #7982

Does your change fix a particular issue?

Fixes #7747 and #7700

Functional testing pending

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• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

Attention: Patch coverage is 58.82353% with 7 lines in your changes missing coverage. Please review.

Project coverage is 59.01%. Comparing base (07c03a8) to head (8eac360).
Report is 4 commits behind head on main.

Files	Patch %	Lines
pkg/cmd/cli/nodeagent/server.go	0.00%	4 Missing ⚠️
pkg/exposer/csi_snapshot.go	72.72%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8109      +/-   ##
==========================================
- Coverage   59.03%   59.01%   -0.03%     
==========================================
  Files         358      358              
  Lines       30141    30154      +13     
==========================================
+ Hits        17795    17796       +1     
- Misses      10907    10917      +10     
- Partials     1439     1441       +2     

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[Lyndon-Li]

@shubham-pampattiwar
I just realized one problem after this PR is merged:

	backupPVCStorageClass := csiExposeParam.StorageClass
	backupPVCReadOnly := false

	if value, exists := csiExposeParam.BackupPVCConfig[csiExposeParam.StorageClass]; exists {
		backupPVCStorageClass = value.StorageClass
		backupPVCReadOnly = value.ReadOnly
	}

Should be modified to:

	backupPVCStorageClass := csiExposeParam.StorageClass
	backupPVCReadOnly := false

	if value, exists := csiExposeParam.BackupPVCConfig[csiExposeParam.StorageClass]; exists {
		if value.StorageClass != "" {
			backupPVCStorageClass = value.StorageClass
		}

		backupPVCReadOnly = value.ReadOnly
	}

value.StorageClass may be empty from the configuration (it is not a must-have field), in this case, we should use the value from csiExposeParam.StorageClass, otherwise, the provision will fail.

I add this change to PR #8115. Just for your information.

[shubham-pampattiwar]

Thank you @Lyndon-Li !