[8.x] Draft Watsonx inference API (#3866)

[lcawl]

Backport

This will backport the following commits from main to 8.x:

• Draft Watsonx inference API (#3866)

Questions ?

Please refer to the Backport tool documentation

[github-actions]

Following you can find the validation results for the APIs you have changed.

API	Status	Request	Response
inference.delete	⚪	Missing test	Missing test
inference.get	🟢	1/1	1/1
inference.inference	⚪	Missing test	Missing test
inference.put_watsonx	⚪	Missing test	Missing test
inference.put	⚪	Missing test	Missing test
inference.stream_inference	⚪	Missing test	Missing test
inference.unified_inference	⚪	Missing test	Missing test
inference.update	⚪	Missing test	Missing test

You can validate these APIs yourself by using the make validate target.