fix(docs): add setuptools explicitly (#2547)

Given the shift to python3.12, we need to explicitly depend on
`setuptools` for the pkg_resources import

## Test Plan

Run 
```
cd local/llama-stack
UV_PROJECT_ENVIRONMENT=/tmp/docs uv sync --frozen --group docs

cd /tmp/docs
uv run python -m sphinx -T -b html -d _build/doctrees -D language=en \
   ~/local/llama-stack/docs/source/ \
  /tmp/docs/html
```

pyproject.toml

@@ -108,6 +108,7 @@ test = [
     "requests",
 ]
 docs = [
+    "setuptools",
     "sphinx-autobuild",
     "myst-parser",
     "sphinx",

uv.lock

@@ -1272,6 +1272,7 @@ docs = [
     { name = "linkify" },
     { name = "myst-parser" },
     { name = "requests" },
+    { name = "setuptools" },
     { name = "sphinx" },
     { name = "sphinx-autobuild" },
     { name = "sphinx-copybutton" },
@@ -1375,6 +1376,7 @@ docs = [
     { name = "linkify" },
     { name = "myst-parser" },
     { name = "requests" },
+    { name = "setuptools" },
     { name = "sphinx" },
     { name = "sphinx-autobuild" },
     { name = "sphinx-copybutton" },