docs: Expand Java DLS Cookbook with additional examples

[domhanak]

Page / section

Reference -> Quarkus Flow Java DSL cookbook

What should change?

Add missing examples:

Raising Explicit Errors
Error Handling (try / catch)
Invoking Subflows
Java Function Calls (function)
Agent-style calls (agent)
Fire-and-Forget Effects (consume)
Data Extraction and Merging (inputFrom, exportAs)

Why?

These examples are part of YAML Cookbook and were not possible to be implemented in #393
We should make the Java DSL Cookbook complete and expand it to cover relevant and interesting use cases.

[ricardozanini]

@domhanak what's the status of this one?

[domhanak]

@ricardozanini I can start working on this, but was just very busy with other work. Most likely we need to move this to new milestone.

[ricardozanini]

Pushed to M 1.0.0.

[ricardozanini]

@domhanak any plans for 1.0.0?