feat: allow building distro with external providers (#1967)

# What does this PR do?

We can now build a distribution that includes external providers.
Closes: https://github.com/meta-llama/llama-stack/issues/1948

## Test Plan

Build a distro with an external provider following the doc instructions.

[//]: # (## Documentation)

Added.

Rendered:


![Screenshot 2025-04-18 at 11 26
39](https://github.com/user-attachments/assets/afcf3d50-8d30-48c3-8d24-06a4b3662881)

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

llama_stack/distribution/build.py

@@ -7,16 +7,16 @@
 import importlib.resources
 import logging
 from pathlib import Path
-from typing import Dict, List
 
 from pydantic import BaseModel
 from termcolor import cprint
 
-from llama_stack.distribution.datatypes import BuildConfig, Provider
+from llama_stack.distribution.datatypes import BuildConfig
 from llama_stack.distribution.distribution import get_provider_registry
 from llama_stack.distribution.utils.exec import run_command
 from llama_stack.distribution.utils.image_types import LlamaStackImageType
 from llama_stack.providers.datatypes import Api
+from llama_stack.templates.template import DistributionTemplate
 
 log = logging.getLogger(__name__)
 
@@ -37,19 +37,24 @@ class ApiInput(BaseModel):
 
 
 def get_provider_dependencies(
-    config_providers: Dict[str, List[Provider]],
+    config: BuildConfig | DistributionTemplate,
 ) -> tuple[list[str], list[str]]:
     """Get normal and special dependencies from provider configuration."""
-    all_providers = get_provider_registry()
+    # Extract providers based on config type
+    if isinstance(config, DistributionTemplate):
+        providers = config.providers
+    elif isinstance(config, BuildConfig):
+        providers = config.distribution_spec.providers
     deps = []
+    registry = get_provider_registry(config)
 
-    for api_str, provider_or_providers in config_providers.items():
-        providers_for_api = all_providers[Api(api_str)]
+    for api_str, provider_or_providers in providers.items():
+        providers_for_api = registry[Api(api_str)]
 
         providers = provider_or_providers if isinstance(provider_or_providers, list) else [provider_or_providers]
 
         for provider in providers:
-            # Providers from BuildConfig and RunConfig are subtly different – not great
+            # Providers from BuildConfig and RunConfig are subtly different – not great
             provider_type = provider if isinstance(provider, str) else provider.provider_type
 
             if provider_type not in providers_for_api:
@@ -71,8 +76,8 @@ def get_provider_dependencies(
     return list(set(normal_deps)), list(set(special_deps))
 
 
-def print_pip_install_help(providers: Dict[str, List[Provider]]):
-    normal_deps, special_deps = get_provider_dependencies(providers)
+def print_pip_install_help(config: BuildConfig):
+    normal_deps, special_deps = get_provider_dependencies(config)
 
     cprint(
         f"Please install needed dependencies using the following commands:\n\nuv pip install {' '.join(normal_deps)}",
@@ -91,7 +96,7 @@ def build_image(
 ):
     container_base = build_config.distribution_spec.container_image or "python:3.10-slim"
 
-    normal_deps, special_deps = get_provider_dependencies(build_config.distribution_spec.providers)
+    normal_deps, special_deps = get_provider_dependencies(build_config)
     normal_deps += SERVER_DEPENDENCIES
 
     if build_config.image_type == LlamaStackImageType.CONTAINER.value: