feat: Adding OpenAI Prompts API (#3319)

# What does this PR do?
This PR adds support for OpenAI Prompts API.

Note, OpenAI does not explicitly expose the Prompts API but instead
makes it available in the Responses API and in the [Prompts
Dashboard](https://platform.openai.com/docs/guides/prompting#create-a-prompt).

I have added the following APIs:
- CREATE
- GET
- LIST
- UPDATE
- Set Default Version

The Set Default Version API is made available only in the Prompts
Dashboard and configures which prompt version is returned in the GET
(the latest version is the default).

Overall, the expected functionality in Responses will look like this:

```python
from openai import OpenAI
client = OpenAI()

response = client.responses.create(
  prompt={
    "id": "pmpt_68b0c29740048196bd3a6e6ac3c4d0e20ed9a13f0d15bf5e",
    "version": "2",
    "variables": {
        "city": "San Francisco",
        "age": 30,
    }
  }
)
```

### Resolves https://github.com/llamastack/llama-stack/issues/3276


## Test Plan
Unit tests added. Integration tests can be added after client
generation.

## Next Steps
1. Update Responses API to support Prompt API
2. I'll enhance the UI to implement the Prompt Dashboard. 
3. Add cache for lower latency

---------

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

llama_stack/apis/resource.py

@@ -19,6 +19,7 @@ class ResourceType(StrEnum):
     benchmark = "benchmark"
     tool = "tool"
     tool_group = "tool_group"
+    prompt = "prompt"
 
 
 class Resource(BaseModel):