chore: first migration to librarian

[jskeet]

This migrates google-area120-tables and google-cloud-config to librarian.

[gemini-code-assist]

Code Review

This pull request migrates the repository configuration to librarian@latest, introducing a new librarian.yaml file and updating .librarian/config.yaml and .librarian/state.yaml. Feedback identifies a critical bug in librarian.yaml where the tag_format includes a space, which is invalid for Git tags. The reviewer also recommends preserving the context of blocked releases from removed TODO comments and ensuring consistent configuration overrides across libraries for better maintainability.

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librarian.yaml (27)

The tag_format value '{name}: v{version}' contains a space, which is invalid for git tags. Git refnames cannot contain whitespace characters. This will cause the release process to fail when attempting to create the tag. Additionally, this format (using a colon and space) is inconsistent with the existing {id}-v{version} format used in the repository.

  tag_format: '{name}-v{version}'

.librarian/config.yaml (19-20)

These TODO comments provide critical context and issue references explaining why specific libraries are currently blocked from release. Removing them makes it difficult for maintainers to track the status of these blocks. If this file is being simplified as part of the migration, please ensure this documentation is moved to librarian.yaml or another persistent location to ensure the reasons for blocking are not lost.

librarian.yaml (56-81)

The configuration for the migrated libraries is inconsistent. For example, google-area120-tables includes default_version but lacks api_shortname_override and product_documentation_override, while google-cloud-config includes the latter two but lacks default_version. To ensure the generated .repo-metadata.json files remain consistent and to improve maintainability, please use a consistent set of overrides for all libraries managed by librarian.