[WIP] feat(generator): add max_metadata_size to gRPC transport templates

[ohmayr]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request updates the gRPC and gRPC asyncio transport templates to include a default grpc.max_metadata_size option set to 32768 bytes. There are no review comments, so I have no feedback to provide.