feat: Add url field to PaginatedResponse and populate it using route … (#2419)

…path


# What does this PR do?

Closes #1847 

Changes:
- llama_stack/apis/common/responses.py: adds optional `url` field to
PaginatedResponse
- llama_stack/distribution/server/server.py: automatically populate the
URL field with route path



## Test Plan

- Built and ran llama stack server using the following cmds:  
  ```bash  
  export INFERENCE_MODEL=llama3.1:8b  
  llama stack build --run --template ollama --image-type container
  llama stack run llama_stack/templates/ollama/run.yaml
  ```
- Ran `curl` to test if we are seeing the `url` param in response:
  ```bash
  curl -X 'GET' \
    'http://localhost:8321/v1/agents' \
    -H 'accept: application/json'
  ```
- Expected and Received Output:
`{"data":[],"has_more":false,"url":"/v1/agents"}`

---------

Co-authored-by: Rohan Awhad <rawhad@redhat.com>

llama_stack/apis/common/responses.py

@@ -23,7 +23,9 @@ class PaginatedResponse(BaseModel):
 
     :param data: The list of items for the current page
     :param has_more: Whether there are more items available after this set
+    :param url: The URL for accessing this list
     """
 
     data: list[dict[str, Any]]
     has_more: bool
+    url: str | None = None