[NEOS-1775] Allow import/export job mappings in grpc format

[nickzelei]

When using the grpc format, the job mappings need to be in the snake_case format. Where as on the frontend using connect, it uses the camelCase format. Why it does this is unusual and unknown. We could explore seeing if there was a way to return them in that format, but would be a breaking API change.

_{From SyncLinear.com | NEOS-1775}

[nickzelei]

Seems to specifically be an encoding issue with the protobuf-es client where it uses lowerCamelCase as its default.

https://github.com/bufbuild/protobuf-es/blob/main/MANUAL.md#field-names
Either we change this to use the same snake_case format, or offer a way to generate the mappings in snake case as an option (or we update the export to export as snake case and then update the import to handle both cases)