SBOM: use annotated data types in Pydantic config

[tiran]

PR #1032 added new Pydantic models that use generic str like upstream_purl and repository_url. Define more specialized, annotated string types with validators to make the schema self-documenting.

Example:

BuildDirectory = typing.Annotated[
    pathlib.Path,
    pydantic.BeforeValidator(_before_builddirectory),
]