seed a load scenario from an OpenAPI specification

Generates an editable load scenario from an OpenAPI spec and loads (registers) it into the registry under "name" in the LOADED state — exactly like PUT /mockserver/loadScenario, it generates no traffic and is allowed even when loadGenerationEnabled is false. One step is produced per OpenAPI operation (in a stable path-then-method order), each with the operation's method and server-prefixed path, a representative request-body example, and a Content-Type header. The spec is accepted identically to PUT /mockserver/openapi/expectation — an inline JSON/YAML payload, a URL, or a file/classpath reference. Target precedence for where each request is sent (carried as the request's Host header and secure flag): an explicit "target" wins, else the spec's servers[0] URL, else the request is left path-only for the operator to edit. When no "profile" is supplied a conservative default is applied (one short constant-VU stage) so the scenario is immediately runnable yet safe — the operator edits it before scaling up. The generated scenario is returned so a client/UI can show and edit it before triggering a run.