librarian: add should parse protobuf language package options

https://github.com/googleapis/librarian/issues/7466 is the motivation for this and it should be expanded to all relevant languages.

Protobuf files can contain a packaging option that provides an explicit value or "hint" for code generators to use in "naming" the generated code. Our `protoc` plugin based GAPIC generators can consume this, but when it is used to inform the output directory and thus the file paths of files we need to encode elsewhere e.g. in release-please configuration, we librarian to understand it as well.

`librarian add` should be able to parse the `.proto` options - either on a per langauge basis or using some centralized lib for doing so - for use in librarian configuration and future implementation e.g. reference in `generate`.

Protobuf docs: https://protobuf.dev/programming-guides/proto3/#packages
AIP docs: https://google.aip.dev/191#packaging-annotations

Start with the `librarian add` entry point and review how it currently reads protobuf-related configuration. Determine how package options should be handled across the relevant languages, then verify that the parsed values are available in librarian configuration for output paths and future `generate` use.

Written by the indexing model from the issue text.