fix(bigquery): field descriptor proto name should not be lowercase

[alvarowolfx]

When converting protobufs back and forth to JSON, the protojson package handles conversion to lowercase camelcase, accordingly to the docs:

• https://protobuf.dev/programming-guides/proto3/#json-options
• Ref: https://github.com/protocolbuffers/protobuf-go/blob/6d0a5dbd95005b70501b4cc2c5124dab07a1f4a0/internal/strs/strings.go#L92

Resolves #8470