[2.0]: Harmonize BOM metadata authorship with the party model

## Describe the feature

The 2.0 draft currently has two parallel representations of "who made this":

1. **Components** use the new party model — `components[].parties[]` with
`roles[]` (`manufacturer`, `author`, `supplier`, …) and an
`organization` / `person` / `system` / `persona` identity
(`cyclonedx-party-2.0.schema.json`, introduced in #930).
2. **BOM metadata** still uses the 1.x discrete fields —
`metadata.manufacturer` (`organizationalEntity`), `metadata.authors[]`
(`organizationalContact`), and `metadata.supplier`
(`cyclonedx-metadata-2.0.schema.json`).

## Possible solutions

Replace metadata.manufacturer / metadata.authors / metadata.supplier
with metadata.parties[].