Add prompt_logprobs and guided_choice to OpenAI completions

This adds the vLLM-specific extra_body parameters of prompt_logprobs
and guided_choice to our openai_completion inference endpoint. The
plan here would be to expand this to support all common optional
parameters of any of the OpenAI providers, allowing each provider to
use or ignore these parameters based on whether their server supports them.

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

docs/_static/llama-stack-spec.html

@@ -9523,6 +9523,15 @@
                     "user": {
                         "type": "string",
                         "description": "(Optional) The user to use"
+                    },
+                    "guided_choice": {
+                        "type": "array",
+                        "items": {
+                            "type": "string"
+                        }
+                    },
+                    "prompt_logprobs": {
+                        "type": "integer"
                     }
                 },
                 "additionalProperties": false,

docs/_static/llama-stack-spec.yaml

@@ -6556,6 +6556,12 @@ components:
         user:
           type: string
           description: (Optional) The user to use
+        guided_choice:
+          type: array
+          items:
+            type: string
+        prompt_logprobs:
+          type: integer
       additionalProperties: false
       required:
         - model