Return model metadata on the duoWorkflows model dimension

The Spend tab needs model names, providers and a self-hosted flag next to each model row. The closed POC fetched the model catalog client side, which put Duo knowledge inside a generic display type and leaned on an admin-only query. This moves the mapping to the API: a new model dimension on the duoWorkflows engine groups by the same value as modelUsed and resolves each raw value to catalog metadata server side, so any consumer renders it generically.

Validated with unit specs for the mapping heuristics and a GraphQL request spec; rubocop clean. Local rspec runs are blocked by a missing gitaly test build in this checkout, so the pipeline is the authoritative run.

Related to !255850 (comment 3843653024)

Related to https://gitlab.com/groups/gitlab-org/-/work_items/23470