feat(orbit): Add Orbit endpoint for named Knowledge Graph queries

What does this MR do and why?

Adds a hidden POST /api/v4/orbit/query/:name endpoint that executes server-defined named queries against the Knowledge Graph gRPC service, instead of clients shipping hard-coded Orbit DSL query strings.

• New Grape endpoint query/:name in ee/lib/api/orbit/data.rb that requires a JSON request body (form encoding stringifies nested parameter values, which the per-query parameter schemas reject) and accepts parameters, response_format, and an optional source_type.
• Gitlab::Workhorse.send_orbit_query gains a query_type: argument and forwards QueryType: named to Workhorse when set.
• Workhorse's Orbit SendQuery injecter maps the new QueryType param to QUERY_TYPE_NAMED on the gRPC ExecuteQueryRequest, defaulting to QUERY_TYPE_JSON as before.

This moves query definitions to live with the server that runs them, so clients invoke a named, structured operation and can no longer drift from the server's DSL grammar/ontology.

References

• gitlab-org/orbit/knowledge-graph#955

Screenshots or screen recordings

Not applicable — backend/API change only.

How to set up and validate locally

1. Ensure the Knowledge Graph gRPC endpoint is configured and the namespace is enabled for Knowledge Graph.

2. Call the endpoint with a JSON body:

   curl --request POST \
     --header "PRIVATE-TOKEN: <token>" \
     --header "Content-Type: application/json" \
     --data '{"parameters": {}, "response_format": "raw"}' \
     "http://gdk.test:3000/api/v4/orbit/query/<query_name>"

3. Verify a non-JSON content type is rejected with 400 JSON request body required (Content-Type: application/json).

MR acceptance checklist

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