feat: add oci genai service as chat inference provider (#3876)

# What does this PR do?
Adds OCI GenAI PaaS models for openai chat completion endpoints.

## Test Plan
In an OCI tenancy with access to GenAI PaaS, perform the following
steps:

1. Ensure you have IAM policies in place to use service (check docs
included in this PR)
2. For local development, [setup OCI
cli](https://docs.oracle.com/en-us/iaas/Content/API/SDKDocs/cliinstall.htm)
and configure the CLI with your region, tenancy, and auth
[here](https://docs.oracle.com/en-us/iaas/Content/API/SDKDocs/cliconfigure.htm)
3. Once configured, go through llama-stack setup and run llama-stack
(uses config based auth) like:
```bash
OCI_AUTH_TYPE=config_file \
OCI_CLI_PROFILE=CHICAGO \
OCI_REGION=us-chicago-1 \
OCI_COMPARTMENT_OCID=ocid1.compartment.oc1..aaaaaaaa5...5a \
llama stack run oci
```
4. Hit the `models` endpoint to list models after server is running:
```bash
curl http://localhost:8321/v1/models | jq
...
{
      "identifier": "meta.llama-4-scout-17b-16e-instruct",
      "provider_resource_id": "ocid1.generativeaimodel.oc1.us-chicago-1.am...q",
      "provider_id": "oci",
      "type": "model",
      "metadata": {
        "display_name": "meta.llama-4-scout-17b-16e-instruct",
        "capabilities": [
          "CHAT"
        ],
        "oci_model_id": "ocid1.generativeaimodel.oc1.us-chicago-1.a...q"
      },
      "model_type": "llm"
},
   ...
```
5. Use the "display_name" field to use the model in a
`/chat/completions` request:
```bash
# Streaming result
curl -X POST http://localhost:8321/v1/chat/completions   -H "Content-Type: application/json"   -d '{
        "model": "meta.llama-4-scout-17b-16e-instruct",
       "stream": true,
       "temperature": 0.9,
      "messages": [
         {
           "role": "system",
           "content": "You are a funny comedian. You can be crass."
         },
          {
           "role": "user",
          "content": "Tell me a funny joke about programming."
         }
       ]
}'

# Non-streaming result
curl -X POST http://localhost:8321/v1/chat/completions   -H "Content-Type: application/json"   -d '{
        "model": "meta.llama-4-scout-17b-16e-instruct",
       "stream": false,
       "temperature": 0.9,
      "messages": [
         {
           "role": "system",
           "content": "You are a funny comedian. You can be crass."
         },
          {
           "role": "user",
          "content": "Tell me a funny joke about programming."
         }
       ]
}'
```
6. Try out other models from the `/models` endpoint.

src/llama_stack/distributions/oci/build.yaml

@@ -0,0 +1,35 @@
+version: 2
+distribution_spec:
+  description: Use Oracle Cloud Infrastructure (OCI) Generative AI for running LLM
+    inference with scalable cloud services
+  providers:
+    inference:
+    - provider_type: remote::oci
+    vector_io:
+    - provider_type: inline::faiss
+    - provider_type: remote::chromadb
+    - provider_type: remote::pgvector
+    safety:
+    - provider_type: inline::llama-guard
+    agents:
+    - provider_type: inline::meta-reference
+    eval:
+    - provider_type: inline::meta-reference
+    datasetio:
+    - provider_type: remote::huggingface
+    - provider_type: inline::localfs
+    scoring:
+    - provider_type: inline::basic
+    - provider_type: inline::llm-as-judge
+    - provider_type: inline::braintrust
+    tool_runtime:
+    - provider_type: remote::brave-search
+    - provider_type: remote::tavily-search
+    - provider_type: inline::rag-runtime
+    - provider_type: remote::model-context-protocol
+    files:
+    - provider_type: inline::localfs
+image_type: venv
+additional_pip_packages:
+- aiosqlite
+- sqlalchemy[asyncio]