fix: openapi: return validation errors to the LLM; improve confirmation prompt

[g-linville]

This PR does two things in the OpenAPI revamp:

• When the LLM provides arguments that do not match the JSONSchema, rather than exiting with an error, the validation errors are returned as a normal message to the LLM so that it can respond by trying again.
• The confirmation prompt shown to the user when running an OpenAPI operation under the OpenAPI revamp is improved to provide details about the specific operation and arguments.