Replace clients with Micronaut Client

[graemerocher]

Feature description

Currently the clients use retrofit, okhttp and others.

We should unify all the clients to use Micronaut HTTP Client. This will allow better insrumentation, and observability.

[graemerocher]

They seem to be progressively migrating to a new abstraction so may be worth waiting for this https://github.com/langchain4j/langchain4j/pull/2991/files

[sdelamo]

they have created an API and they now ship an implementation based on the built-in JDK HTTP Client

https://github.com/langchain4j/langchain4j/tree/main/http-clients/langchain4j-http-client-jdk