Spring-ai Change the Prompt's modelOptions return to ChatOptions

Change the Prompt's modelOptions return to ChatOptions, This simplifies the code

Comment From: tzolov

Thank you @luocongqiu This was an annoying omission on the API model that we have not addressed so far.

Btw what name can I use for the @authors javadoc?

Comment From: tzolov

Thank you @luocongqiu I've used your github handle as a javadoc author. Feel free change it in another PR.

rebased, cleaned and merged at 75d68662ae24d2e480291f587b9d02a273166958