docs: part 1 - fix warnings in documentation generation (#2861)

**Description**
This PR removes some of the warnings when uv builds the docs
- Errors appear when generating docs about .md files not appearing in
toctree. ~~Adding content to the `providers-gen.py ` file that adds `---
orphan: true ---` to to each file.~~. Added a toctree generator to the
`providers-gen.py` file, this gets rid of the errors in the builds.
- Deletes the `_openai_compat` files, extension of PR #2849
- Adds the `files` APIs section to the `providers` toctree on the index
page
- Manually adds the `--- orphan: true ---` to the advanced apis. Ill try
to find a way to modify the providers code gen so it automatically adds
it, but this fixes the errors.
- Adds the `testing.md` to the `contributing` toctree
- Adds `starting_llama_stack_server.md` to `distributions` toctree

There are some other warnings im still looking at but this PR gets rid
of most of the toctree errors
Theres also an issue with the actual distribution-codegen that I can
investigate in another PR. Opened a bug for it here #2873

docs/source/distributions/index.md

@@ -9,6 +9,7 @@ This section provides an overview of the distributions available in Llama Stack.
 list_of_distributions
 building_distro
 customizing_run_yaml
+starting_llama_stack_server
 importing_as_library
 configuration
 ```