[docs] add openapi spec to docs (#508)

# What does this PR do?
- modify openapi generator to add coming soon tag for unimplemented api
- sphinx-redocs extension for openapi spec to readthedocs page

## Test Plan



https://github.com/user-attachments/assets/b4c7eebc-2361-4198-a987-dbfbcff914cf






## Before submitting

- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [ ] Ran pre-commit to handle lint / formatting issues.
- [ ] Read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

docs/source/conf.py

@@ -25,6 +25,7 @@ extensions = [
     "sphinx_copybutton",
     "sphinx_tabs.tabs",
     "sphinx_design",
+    "sphinxcontrib.redoc",
 ]
 myst_enable_extensions = ["colon_fence"]
 
@@ -82,3 +83,18 @@ html_theme_options = {
 html_static_path = ["../_static"]
 # html_logo = "../_static/llama-stack-logo.png"
 html_style = "../_static/css/my_theme.css"
+
+redoc = [
+    {
+        "name": "Llama Stack API",
+        "page": "references/api_reference/index",
+        "spec": "../resources/llama-stack-spec.yaml",
+        "opts": {
+            "suppress-warnings": True,
+            # "expand-responses": ["200", "201"],
+        },
+        "embed": True,
+    },
+]
+
+redoc_uri = "https://cdn.redoc.ly/redoc/latest/bundles/redoc.standalone.js"