Fix OpenAI API response format handling

This fixes the schema of OpenAI API chat completion response formats,
including how those response formats (and other nested parameters in
the chat completion request) get translated into paramters for calls
to the backend OpenAI-compatible providers.

Signed-off-by: Ben Browning <bbrownin@redhat.com>

docs/_static/llama-stack-spec.yaml

@@ -6157,6 +6157,29 @@ components:
       required:
         - url
       title: OpenAIImageURL
+    OpenAIJSONSchema:
+      type: object
+      properties:
+        name:
+          type: string
+        description:
+          type: string
+        strict:
+          type: boolean
+        schema:
+          type: object
+          additionalProperties:
+            oneOf:
+              - type: 'null'
+              - type: boolean
+              - type: number
+              - type: string
+              - type: array
+              - type: object
+      additionalProperties: false
+      required:
+        - name
+      title: OpenAIJSONSchema
     OpenAIMessageParam:
       oneOf:
         - $ref: '#/components/schemas/OpenAIUserMessageParam'
@@ -6172,6 +6195,53 @@ components:
           assistant: '#/components/schemas/OpenAIAssistantMessageParam'
           tool: '#/components/schemas/OpenAIToolMessageParam'
           developer: '#/components/schemas/OpenAIDeveloperMessageParam'
+    OpenAIResponseFormatJSONObject:
+      type: object
+      properties:
+        type:
+          type: string
+          const: json_object
+          default: json_object
+      additionalProperties: false
+      required:
+        - type
+      title: OpenAIResponseFormatJSONObject
+    OpenAIResponseFormatJSONSchema:
+      type: object
+      properties:
+        type:
+          type: string
+          const: json_schema
+          default: json_schema
+        json_schema:
+          $ref: '#/components/schemas/OpenAIJSONSchema'
+      additionalProperties: false
+      required:
+        - type
+        - json_schema
+      title: OpenAIResponseFormatJSONSchema
+    OpenAIResponseFormatParam:
+      oneOf:
+        - $ref: '#/components/schemas/OpenAIResponseFormatText'
+        - $ref: '#/components/schemas/OpenAIResponseFormatJSONSchema'
+        - $ref: '#/components/schemas/OpenAIResponseFormatJSONObject'
+      discriminator:
+        propertyName: type
+        mapping:
+          text: '#/components/schemas/OpenAIResponseFormatText'
+          json_schema: '#/components/schemas/OpenAIResponseFormatJSONSchema'
+          json_object: '#/components/schemas/OpenAIResponseFormatJSONObject'
+    OpenAIResponseFormatText:
+      type: object
+      properties:
+        type:
+          type: string
+          const: text
+          default: text
+      additionalProperties: false
+      required:
+        - type
+      title: OpenAIResponseFormatText
     OpenAISystemMessageParam:
       type: object
       properties:
@@ -6331,9 +6401,7 @@ components:
           description: >-
             (Optional) The penalty for repeated tokens
         response_format:
-          type: object
-          additionalProperties:
-            type: string
+          $ref: '#/components/schemas/OpenAIResponseFormatParam'
           description: (Optional) The response format to use
         seed:
           type: integer