feat: consolidate most distros into "starter" (#2516)

# What does this PR do?

* Removes a bunch of distros
* Removed distros were added into the "starter" distribution
* Doc for "starter" has been added
* Partially reverts https://github.com/meta-llama/llama-stack/pull/2482
  since inference providers are disabled by default and can be turned on
  manually via env variable.
* Disables safety in starter distro

Closes: https://github.com/meta-llama/llama-stack/issues/2502.

~Needs: https://github.com/meta-llama/llama-stack/pull/2482 for Ollama
to work properly in the CI.~

TODO:

- [ ] We can only update `install.sh` when we get a new release.
- [x] Update providers documentation
- [ ] Update notebooks to reference starter instead of ollama

Signed-off-by: Sébastien Han <seb@redhat.com>

llama_stack/distribution/stack.py

@@ -98,6 +98,10 @@ async def register_resources(run_config: StackRunConfig, impls: dict[Api, Any]):
 
         method = getattr(impls[api], register_method)
         for obj in objects:
+            # Do not register models on disabled providers
+            if hasattr(obj, "provider_id") and obj.provider_id is not None and obj.provider_id == "__disabled__":
+                logger.debug(f"Skipping {rsrc.capitalize()} registration for disabled provider.")
+                continue
             # In complex templates, like our starter template, we may have dynamic model ids
             # given by environment variables. This allows those environment variables to have
             # a default value of __disabled__ to skip registration of the model if not set.
@@ -106,6 +110,7 @@ async def register_resources(run_config: StackRunConfig, impls: dict[Api, Any]):
                 and obj.provider_model_id is not None
                 and "__disabled__" in obj.provider_model_id
             ):
+                logger.debug(f"Skipping {rsrc.capitalize()} registration for disabled model.")
                 continue
             # we want to maintain the type information in arguments to method.
             # instead of method(**obj.model_dump()), which may convert a typed attr to a dict,
@@ -149,6 +154,25 @@ def replace_env_vars(config: Any, path: str = "") -> Any:
         result = []
         for i, v in enumerate(config):
             try:
+                # Special handling for providers: first resolve the provider_id to check if provider
+                # is disabled so that we can skip config env variable expansion and avoid validation errors
+                if isinstance(v, dict) and "provider_id" in v:
+                    try:
+                        resolved_provider_id = replace_env_vars(v["provider_id"], f"{path}[{i}].provider_id")
+                        if resolved_provider_id == "__disabled__":
+                            logger.debug(
+                                f"Skipping config env variable expansion for disabled provider: {v.get('provider_id', '')}"
+                            )
+                            # Create a copy with resolved provider_id but original config
+                            disabled_provider = v.copy()
+                            disabled_provider["provider_id"] = resolved_provider_id
+                            result.append(disabled_provider)
+                            continue
+                    except EnvVarError:
+                        # If we can't resolve the provider_id, continue with normal processing
+                        pass
+
+                # Normal processing for non-disabled providers
                 result.append(replace_env_vars(v, f"{path}[{i}]"))
             except EnvVarError as e:
                 raise EnvVarError(e.var_name, e.path) from None