Vertex RAG Corpus can be with RagResource in VertexAiGeminiChatModel

Please do a quick search on GitHub issues first, the feature you are about to request might have already been requested.

Expected Behavior

VertexAiGeminiChatModel passes RagCorpus as Retrieval.

Current Behavior

Now, VertexAiGeminiChatModel.createGeminiRequest() supports functions definitions, and GoogleSearch only.

Context

How has this issue affected you?
There seems to be no way to use Rag Corpus in GCP

What are you trying to accomplish?
I am trying to make the call with

"retrieval": {
        "vertexRagStore": {
          "ragResources": [
            {
              "ragCorpus": "projects/{project_id}/locations/{localtion}/ragCorpora/{rag_corpus_id}"
            }
          ],
          "ragRetrievalConfig": {
            "filter": {
              "vectorSimilarityThreshold": 0.5
            },
            "topK": 3
          }
        }
      }

What other alternatives have you considered?
I have considered using native google genai SDK

Are you aware of any workarounds?

Adding the following lines will make it work.

line 714- in VertexAiGeminiChatModel.java

		if (prompt.getOptions() instanceof VertexAiGeminiChatOptions options && !StringUtil.isNullOrEmpty(options.getRagCorpus())) {
			final Tool ragCorpusTool = Tool.newBuilder()
					.setRetrieval(
							Retrieval.newBuilder().setVertexRagStore(VertexRagStore.newBuilder()
									.addRagResources(
											0,
											VertexRagStore.RagResource.newBuilder()
													.setRagCorpus(options.getRagCorpus())
													.build()
									).build()
							).build()
					).build();
			tools.add(ragCorpusTool);
		}

line 152- in VertexAiGeminiChatOptions.java

/**
	 * Use Google RAG Corpus feature
	 */
	@JsonIgnore
	private String ragCorpus;

...
// add Getter and Setter
...

This works with other tools correctly.

Start by searching existing GitHub issues, then inspect VertexAiGeminiChatModel.java around line 714 and VertexAiGeminiChatOptions.java around line 152. Trace how existing function definitions and GoogleSearch tools are added, and use the provided RagResource example as the expected behavior. Done means VertexAiGeminiChatModel can send a Vertex RAG Corpus while preserving other tools.