feat: adding endpoints for files and uploads (#1070)

Summary:
Adds spec definitions for file uploads operations.

This API focuses around two high level operations:
* Initiating and managing upload session
* Accessing uploaded file information

Usage examples:

To start a file upload session:
```
curl -X POST https://localhost:8321/v1/files \
-d '{
   "key": "image123.jpg',
   "bucket": "images",
   "mime_type": "image/jpg",
   "size": 12345
}'

# Returns
{
  “id”: <session_id>
  “url”: “https://localhost:8321/v1/files/session:<session_id>”,
  "offset": 0,
  "size": 12345
}

```

To upload file content to an existing session
```
curl -i -X POST "https://localhost:8321/v1/files/session:<session_id> \
  --data-binary @<path_to_local_file>

# Returns
{
  "key": "image123.jpg",
  "bucket": "images",
  "mime_type": "image/jpg",
  "bytes": 12345,
  "created_at": 1737492240
}

# Implementing on server side (Flask example for simplicity):
@app.route('/uploads/{upload_id}', methods=['POST'])
def upload_content_to_session(upload_id):
    try:
        # Get the binary file data from the request body
        file_data = request.data

        # Save the file to disk
        save_path = f"./uploads/{upload_id}"
        with open(save_path, 'wb') as f:
            f.write(file_data)
        return {__uploaded_file_json__}, 200
    except Exception as e:
        return 500

```

To read information about an existing upload session
```
curl -i -X GET "https://localhost:8321/v1/files/session:<session_id>

# Returns
{
  “id”: <session_id>
  “url”: “https://localhost:8321/v1/files/session:<session_id>”,
  "offset": 1024,
  "size": 12345
}
```

To list buckets
```
GET /files

# Returns
{
  "data": [
     {"name": "bucket1"},
     {"name": "bucket2"},
   ]
}
```

To list all files in a bucket
```
GET /files/{bucket}

# Returns
{
  "data": [
    {
      "key": "shiba.jpg",
      "bucket": "dogs",
      "mime_type": "image/jpg",
      "bytes": 82334,
      "created_at": 1737492240,
    },
    {
      "key": "persian_cat.jpg",
      "mime_type": "image/jpg",
      "bucket": "cats",
      "bytes": 39924,
      "created_at": 1727493440,
    },
  ]
}
```

To get specific file info
```
GET /files/{bucket}/{key}

{
  "key": "shiba.jpg",
  "bucket": "dogs",
  "mime_type": "image/jpg",
  "bytes": 82334,
  "created_at": 1737492240,
}

```

To delete specific file
```
DELETE /files/{bucket}/{key}

{
  "key": "shiba.jpg",
  "bucket": "dogs",
  "mime_type": "image/jpg",
  "bytes": 82334,
  "created_at": 1737492240,
}

```

llama_stack/schema_utils.py

@@ -19,6 +19,7 @@ class WebMethod:
     request_examples: Optional[List[Any]] = None
     response_examples: Optional[List[Any]] = None
     method: Optional[str] = None
+    raw_bytes_request_body: Optional[bool] = False
 
 
 def webmethod(
@@ -27,6 +28,7 @@ def webmethod(
     public: Optional[bool] = False,
     request_examples: Optional[List[Any]] = None,
     response_examples: Optional[List[Any]] = None,
+    raw_bytes_request_body: Optional[bool] = False,
 ) -> Callable[[T], T]:
     """
     Decorator that supplies additional metadata to an endpoint operation function.
@@ -44,6 +46,7 @@ def webmethod(
             public=public or False,
             request_examples=request_examples,
             response_examples=response_examples,
+            raw_bytes_request_body=raw_bytes_request_body,
         )
         return cls