Introduce Agentic DSL

[ricardozanini]

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What this PR does / why we need it:

Special notes for reviewers:

Additional information (if needed):

[ricardozanini]

The PR is ready, but it requires the work done here: https://github.com/langchain4j/langchain4j/blob/agentic-poc/langchain4j-agentic/

@mariofusco fyi - I'll open a PR on your branch with this DSL. You can see the tests in this PR, but you can do things like:

    Agents.MovieExpert a1 = AgentsUtils.newMovieExpert();
    Agents.MovieExpert a2 = AgentsUtils.newMovieExpert();
    Agents.MovieExpert a3 = AgentsUtils.newMovieExpert();

    Workflow wf = AgenticWorkflowBuilder.workflow().tasks(d -> d.parallel(a1, a2, a3)).build();
            
     // and Run it:
     try (WorkflowApplication app = WorkflowApplication.builder().build()) {
         app.workflowDefinition(workflow)
                  .instance(input).start().get().asJavaObject()
     }

You get "for free" all the control flows from the CNCF Workflow Spec, such as then, set, callHTTP, and so on.

One could do:

Workflow wf = AgenticWorkflowBuilder.workflow().tasks(d -> 
    d.parallel("p", a1, a2, a3).compete(false))
     .callHTTP(c -> c.url("http://endpoint")).build();

Of course, we can make the Agentic DSL even more friendly to LC4J use cases - the intention of this module is to be built on top of the langchain4j-agentic. So we are free to add all the shortcuts/generics/types required.