Add new openapi spec for Watsonx.ai extension

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Hi, I have created a new all-in-one openapi spec for Watsonx.ai extension, that able to connect wxAssistant/wxOrchestrate to external AI services and model/template deployed into watsonx.ai runtime.

The new openapi spec including 6 path:

• generate text with wx.ai
• generate text (stream)
• generate text with deployed model/template
• generate text with deployed model/template (stream)
• generate text with deployed AI service
• generate text with deployed AI service (stream)

This could be useful for everyone who wants to use external models on watsonx.ai, skip tuning prompts inside wxA, or conduct a RAG pipeline inside watsonx.ai

I want to add this to https://github.com/watson-developer-cloud/assistant-toolkit/tree/master/integrations/extensions/starter-kits/language-model-watsonx as an advanced usecase.