[java-bigquery] Make build time only dependencies optional

It would be cool if dependencies only needed at build time were marked as optional. That would reduce the amount of dependencies that are pulled when depending on this project. Thanks !

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Start by locating the java-bigquery module's build configuration and reviewing which dependencies are used only during the build. Check how those dependencies are exposed to consumers, then verify that build-time-only dependencies are no longer pulled transitively and that the module still builds successfully.

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