Do not persist VolumeSnapshot and VolumeSnapshotContent for snapshot DataMover case

[blackpiglet]

1. Because VolumeSnapshot and VolumeSnapshotContent CRs are not kept after the backup is completed, don't persist them in the backup metadata.
2. Add some builder methods needed by the CSI plugin.

Thank you for contributing to Velero!

Please add a summary of your change

Does your change fix a particular issue?

Fixes #6118

Please indicate you've done the following:

• 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-commenter]

Codecov Report

Merging #6366 (0f53fd5) into main (9951358) will decrease coverage by 0.03%.
The diff coverage is 17.85%.

@@            Coverage Diff             @@
##             main    #6366      +/-   ##
==========================================
- Coverage   48.10%   48.08%   -0.03%     
==========================================
  Files         227      227              
  Lines       23316    23342      +26     
==========================================
+ Hits        11217    11224       +7     
- Misses      11250    11265      +15     
- Partials      849      853       +4     

Impacted Files	Coverage Δ
pkg/cmd/util/output/backup_describer.go	0.00% <0.00%> (ø)
pkg/cmd/util/output/backup_structured_describer.go	0.00% <0.00%> (ø)
pkg/cmd/cli/backup/create.go	21.25% <22.22%> (-0.29%)	⬇️
pkg/controller/backup_controller.go	57.32% <100.00%> (-0.03%)	⬇️

... and 1 file with indirect coverage changes