feat(firestore): return listBackupsResponse from firestore:backups:list --json

[google-labs-jules]

This change modifies the firestore:backups:list command to return the full listBackupsResponse object when the --json flag is specified. This is a breaking change, but it provides more information to the user and addresses a TODO in the code.

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PR created automatically by Jules for task 12220291000041495517

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