Modify help message of parameter --snapshot-volumes

[blackpiglet]

Clarify the help message for the default value of parameter --snapshot-volumes, when it's not set.

Signed-off-by: Xun Jiang blackpiglet@gmail.com

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Does your change fix a particular issue?

Fixes #5019

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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-commenter]

Codecov Report

Merging #5350 (56d032d) into main (4768c2a) will not change coverage.
The diff coverage is 0.00%.

❗ Current head 56d032d differs from pull request most recent head d134783. Consider uploading reports for the commit d134783 to get more accurate results

@@           Coverage Diff           @@
##             main    #5350   +/-   ##
=======================================
  Coverage   40.81%   40.81%           
=======================================
  Files         234      234           
  Lines       20275    20275           
=======================================
  Hits         8276     8276           
  Misses      11396    11396           
  Partials      603      603           

Impacted Files	Coverage Δ
pkg/cmd/cli/backup/create.go	22.32% <0.00%> (ø)

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[danfengliu]

LGTM