Add E2E cases for BackupRepository configuration

[blackpiglet]

Describe the problem/challenge you have

Should add new E2E automation cases to verify the feature of the BackupRepository configuration.

The feature's original issue is #7620.
The feature's design is https://github.com/vmware-tanzu/velero/blob/main/design/Implemented/backup-repo-config.md.

Describe the solution you'd like

Anything else you would like to add:

Environment:

• Velero version (use velero version):
• Kubernetes version (use kubectl version):
• Kubernetes installer & version:
• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release):

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[reasonerjt]

Is it a good way to verify it in E2E?

[blackpiglet]

By far, only the cache size is configurable in BackupRepository, and there is no good way to check its value from the Velero CLI side. It's more Kopia-related, then it's good to close this issue.
Let's add the E2E cases when there is a concrete scenario.

[reasonerjt]

The configuration setting may be hard to verify via E2E but let's make sure that the configuration is set in the regular regression test.