[DOC] Invoke OpenAPI Services from Workflows

User Story: As a workflow developer, I want to make HTTP requests via OpenAPI specification files so that I can compose HTTP services in my cluster.

Additional Information: This use case might mention OpenShift Serverless (Knative Serving and Knative Functions) as examples of how to invoke remote services via OpenAPI.

Feature: GA

Upstream documentation:

• https://openshift-knative.github.io/docs/docs/latest/serverless-logic/service-orchestration/orchestration-of-openapi-based-services.html
• https://openshift-knative.github.io/docs/docs/latest/serverless-logic/service-orchestration/configuring-openapi-services-endpoints.html