Added backupController's UT to test the prepareBackupRequest() method BackupStorageLocation processing logic

[niulechuan]

Please add a summary of your change

Added backupController's UT to test the prepareBackupRequest() method BackupStorageLocation processing logic. This important test was missing in the original UT.

The current test for prepareBackupRequest() is:
1. Test the backupLocationLabel is set correctly. lack of error msg testing, non-default backupStorageLocaltion testing.
2. Is backupTTL set correctly.

Does your change fix a particular issue?

Fixes #(issue)

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 #5362 (a5f1e7a) into main (ac2bb3e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #5362   +/-   ##
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  Coverage   40.61%   40.61%           
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  Files         234      234           
  Lines       20293    20293           
=======================================
  Hits         8241     8241           
  Misses      11450    11450           
  Partials      602      602           

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[niulechuan]

/kind changelog-not-required

[reasonerjt]

LGTM, thanks!