Add OCI Generative AI new model support (#22880)

- [x] PR title: 
community: Add OCI Generative AI new model support
 
- [x] PR message:
- Description: adding support for new models offered by OCI Generative
AI services. This is a moderate update of our initial integration PR
16548 and includes a new integration for our chat models under
/langchain_community/chat_models/oci_generative_ai.py
    - Issue: NA
- Dependencies: No new Dependencies, just latest version of our OCI sdk
    - Twitter handle: NA


- [x] Add tests and docs: 
  1. we have updated our unit tests
2. we have updated our documentation including a new ipynb for our new
chat integration


- [x] Lint and test: 
 `make format`, `make lint`, and `make test` run successfully

---------

Co-authored-by: RHARPAZ <RHARPAZ@RHARPAZ-5750.us.oracle.com>
Co-authored-by: Arthur Cheng <arthur.cheng@oracle.com>

libs/community/tests/unit_tests/llms/test_oci_generative_ai.py

@@ -4,7 +4,7 @@ from unittest.mock import MagicMock
 import pytest
 from pytest import MonkeyPatch
 
-from langchain_community.llms import OCIGenAI
+from langchain_community.llms.oci_generative_ai import OCIGenAI
 
 
 class MockResponseDict(dict):
@@ -16,12 +16,12 @@ class MockResponseDict(dict):
 @pytest.mark.parametrize(
     "test_model_id", ["cohere.command", "cohere.command-light", "meta.llama-2-70b-chat"]
 )
-def test_llm_call(monkeypatch: MonkeyPatch, test_model_id: str) -> None:
-    """Test valid call to OCI Generative AI LLM service."""
+def test_llm_complete(monkeypatch: MonkeyPatch, test_model_id: str) -> None:
+    """Test valid completion call to OCI Generative AI LLM service."""
     oci_gen_ai_client = MagicMock()
     llm = OCIGenAI(model_id=test_model_id, client=oci_gen_ai_client)
 
-    provider = llm._get_provider()
+    provider = llm.model_id.split(".")[0].lower()
 
     def mocked_response(*args):  # type: ignore[no-untyped-def]
         response_text = "This is the completion."
@@ -71,6 +71,5 @@ def test_llm_call(monkeypatch: MonkeyPatch, test_model_id: str) -> None:
             )
 
     monkeypatch.setattr(llm.client, "generate_text", mocked_response)
-
     output = llm.invoke("This is a prompt.", temperature=0.2)
     assert output == "This is the completion."