[azopenai] Rename package

[richardpark-msft]

The current package is under cognitiveservices/azopenai, but we want to move it to ai/azopenai

The process:

1. Deprecate the old package
2. Get OpenAI to update the link to our SDK on their libraries page.
3. Incorrectly submit issue to delist old package from pkg.go.dev: link
4. Retract the package: [azopenai] Retract old congitiveservices/azopenai package. #21350
5. Delete the old source code after releasing one more time.