[sdk-platform-java] Replace Owlbot (owlbot copy-code) in hermetic build

In hermetic build, Owlbot is used to copy pre-processed library to its final destination for post-processing. It needs a configuration file, `.OwlBot-hermetic.yaml` to specify how to copy generated files to the destination.

The configuration cause some confusion, e.g., after adding a module in a library, we also need to modify the configuration so that Owlbot can copy the newly generated module to its destination ([commit](https://github.com/googleapis/google-cloud-java/pull/11284/commits/0218a213dc3d2ce4fe49e1b1bd7a9bea1aadc468)).

In addition, we need to install npm, nodejs and git in the docker image to support Owlbot, which may introduce security vulnerabilities.

We should replace Owlbot copy-code function with our own implementation and remove the configuration file.

Note that Owlbot has more functions and handwritten libraries may contain customizations, we need to support them as well.