Make it possible to use a CustomMessage with Ollama

[fjuma]

Once langchain4j/langchain4j#2399 is included in the next LangChain4j release, we can update the Ollama MessageMapper to make it possible to make use of a dev.langchain4j.data.message.CustomMessage.

CustomMessages can be useful for some models like Granite Guardian that make use of non-standard messages with a "context" role to assess the retrieved context used for Retrieval-Augmented Generation (RAG).

[fjuma]

I can submit a PR for this.

@geoand Just wanted to check with you first. For something like this that depends on a change that will be included in the next LangChain4j release, is it ok to submit a draft pull request against Quarkus LangChain4j now or is it better to wait for the change to become available in a LangChain4j release first and then submit the PR against Quarkus LangChain4j after that?

[geoand]

I would just go ahead and do whatever unblocks you quickest.
We can figure out converging later

[fjuma]

Sounds good, thanks for the quick response! I'll likely submit a draft PR for this.

[geoand]

👌