Add credential file store in the backup deletion controller.

[blackpiglet]

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

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Please add a summary of your change

Add credential store in backup deletion controller to support VSL credential.

I followed these steps of v1.10 Velero manual test to verify VSL credential feature.

• Prepare workload as target to backup;
• Modify the default credential cloud-credentials to wrong value.
• Backup should fail.
• Create a new secret with correct credentials, and patch BSL and VSL to use it.

# Handle VSL credential
kubectl create secret generic -n velero --from-file=/Users/jxun/Documents/credentials-velero-gcp vsl-credential
 
kubectl -n velero patch VolumeSnapshotLocation default -p '{"spec":{"credential":{"name":"vsl-credential", "key":"credentials-velero-gcp"}}}' --type=merge

# Handel BSL credential
kubectl create secret generic -n velero --from-file=/Users/jxun/Documents/credentials-velero-gcp bsl-credential
 
kubectl -n velero patch BackupStorageLocation default -p '{"spec":{"credential":{"name":"bsl-credential", "key":"credentials-velero-gcp"}}}' --type=merge

After BSL and VSL's credential modification, backup can be created successfully, but backup deletion would fail with something similar to "unable to read credential from environment variable GOOGLE_APPLICATION_CREDENTIALS".

This is caused by BackupDeletionController didn't have the secret credetial store to read secret. I didn't trigger this error during GCP supporting VSL credential PR, because BSL's credential is not modified during verification.

Does your change fix a particular issue?

Fixes #4862

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 #5521 (41fc641) into main (150570f) will decrease coverage by 0.06%.
The diff coverage is 37.50%.

@@            Coverage Diff             @@
##             main    #5521      +/-   ##
==========================================
- Coverage   40.74%   40.68%   -0.07%     
==========================================
  Files         238      238              
  Lines       20553    20559       +6     
==========================================
- Hits         8375     8364      -11     
- Misses      11563    11578      +15     
- Partials      615      617       +2     

Impacted Files	Coverage Δ
pkg/cmd/server/server.go	6.57% <0.00%> (-0.02%)	⬇️
pkg/controller/backup_deletion_controller.go	57.26% <42.85%> (-0.26%)	⬇️
pkg/uploader/provider/kopia.go	52.84% <0.00%> (-4.07%)	⬇️
pkg/restore/restore.go	64.16% <0.00%> (-0.57%)	⬇️

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