feat: add controller, test and mock support for GKEBackupBackup

[jingyih]

There are too many diff in the GKE container, causing GitHub's diff system to fail. Here is the actual diff between the real and mock for GKEBackupBackup: https://www.diffchecker.com/cRxkr5KT/

[google-oss-prow]

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[jingyih]

/assign @yuwenma