feat: Add metadata field to request and response (#4237)

This changes adds Optional metadata field to OpenAI compatible request
and response object.

fixes: #3564

Signed-off-by: Abhishek Bongale <abhishekbongale@outlook.com>
Co-authored-by: Ashwin Bharambe <ashwin.bharambe@gmail.com>

docs/static/experimental-llama-stack-spec.yaml

@@ -3336,6 +3336,12 @@ components:
           anyOf:
           - type: integer
           - type: 'null'
+        metadata:
+          anyOf:
+          - additionalProperties:
+              type: string
+            type: object
+          - type: 'null'
         input:
           items:
             anyOf:
@@ -3736,6 +3742,12 @@ components:
           anyOf:
           - type: integer
           - type: 'null'
+        metadata:
+          anyOf:
+          - additionalProperties:
+              type: string
+            type: object
+          - type: 'null'
       type: object
       required:
       - created_at