feat: Update transaction.proto to include different lock modes (googleapis#2112)

* feat: Update transaction.proto to include different lock modes

PiperOrigin-RevId: 481838475

Source-Link: googleapis/googleapis@922f1f3

Source-Link: https://github.com/googleapis/googleapis-gen/commit/bf32c6e413d4d7fd3c99b725fab653eb983d9dd6
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