Move the `LogError` trait from `oak_utils` to `oak_functions_logger` crate

[conradgrobler]

The oak_utils crate contains code generation utilities, so it intended to be used as a build-time-only depenndency. The LogError trait is used at runtime so should be moved to another crate so that dependencies on oak_utils can become build dependencies again.

The oak_functions_logger crate is probably the most appropriate, as it already contains a logging-related trait.

[conradgrobler]

It might also be useful to have a unified ExtensionLogger trait, rather than just an ErrorLogger that can be implemented by all extensions, providing log_error, log_warn, log_info and log_debug

[conradgrobler]

This trait no longer exists and the oak_utils crate has been renamed to oak_grpc_utils and now only contains GRPC and proto code generation logic.