fix: [Orchestration] prompts with template references

[n-o-u-r-h-a-n]

Context

AI/ai-sdk-java-backlog#264.

var template = TemplateConfig.reference().byId("21cb1358-0bf1-4f43-870b-00f14d0f9f16");
var configWithTemplate = config.withTemplateConfig(template);

var prompt = new OrchestrationPrompt("Foo bar");

var response = client.chatCompletion(prompt, configWithTemplate);

In this case, the prompt message Foo bar is simply ignored without warning or error.

The above code should throw an exception due to improper use.

Feature scope:

• bug fixed and test created

Definition of Done

• Functionality scope stated & covered
• Tests cover the scope above
• Relevant E2E tests are green (at least locally)
• Error handling created / updated & covered by the tests above
• Aligned changes with the JavaScript SDK
• Documentation updated
• Release notes updated

[n-o-u-r-h-a-n]

The backlog item included //TODO: extend this ticket to also cover orchestration config ref

However, after investigation there is no a current bug in orchestration config reference as prompt is embedded in the reference and there exists no public API to inject a user message into the prompt.

[CharlesDuboisSAP]

We would prefer to have the v2 API restrict inputing a prompt with a prompt reference rather than throwing.

• https://github.com/SAP/ai-sdk-java-backlog/issues/430
  Blocking this PR for now

[n-o-u-r-h-a-n]

We would prefer to have the v2 API restrict inputing a prompt with a prompt reference rather than throwing.

• [SDK v2] Align method names in OrchestrationClient ai-sdk-java-backlog#430
  Blocking this PR for now

Here is the new PR which introduces the new v2 api.