feat: add --run to llama stack build (#1156)

# What does this PR do?

--run runs the stack that was just build using the same arguments during
the build process (image-name, type, etc)

This simplifies the workflow a lot and makes the UX better for most
local users trying to get started rather than having to match the flags
of the two commands (build and then run)

Also, moved `ImageType` to distribution.utils since there were circular
import errors with its old location

## Test Plan

tested locally using the following command: 

`llama stack build --run --template ollama --image-type venv`

Signed-off-by: Charlie Doern <cdoern@redhat.com>

llama_stack/distribution/utils/exec.py

@@ -12,8 +12,78 @@ import signal
 import subprocess
 import sys
 
+from termcolor import cprint
+
 log = logging.getLogger(__name__)
 
+import importlib
+import json
+from pathlib import Path
+
+from llama_stack.distribution.utils.image_types import ImageType
+
+
+def formulate_run_args(image_type, image_name, config, template_name) -> list:
+    if image_type == ImageType.container.value or config.container_image:
+        script = importlib.resources.files("llama_stack") / "distribution/start_container.sh"
+        image_name = f"distribution-{template_name}" if template_name else config.container_image
+        run_args = [script, image_name]
+    elif image_type == ImageType.conda.value:
+        current_conda_env = os.environ.get("CONDA_DEFAULT_ENV")
+        image_name = image_name or current_conda_env
+        if not image_name:
+            cprint(
+                "No current conda environment detected, please specify a conda environment name with --image-name",
+                color="red",
+            )
+            return
+
+        def get_conda_prefix(env_name):
+            # Conda "base" environment does not end with "base" in the
+            # prefix, so should be handled separately.
+            if env_name == "base":
+                return os.environ.get("CONDA_PREFIX")
+            # Get conda environments info
+            conda_env_info = json.loads(subprocess.check_output(["conda", "info", "--envs", "--json"]).decode())
+            envs = conda_env_info["envs"]
+            for envpath in envs:
+                if envpath.endswith(env_name):
+                    return envpath
+            return None
+
+        print(f"Using conda environment: {image_name}")
+        conda_prefix = get_conda_prefix(image_name)
+        if not conda_prefix:
+            cprint(
+                f"Conda environment {image_name} does not exist.",
+                color="red",
+            )
+            return
+
+        build_file = Path(conda_prefix) / "llamastack-build.yaml"
+        if not build_file.exists():
+            cprint(
+                f"Build file {build_file} does not exist.\n\nPlease run `llama stack build` or specify the correct conda environment name with --image-name",
+                color="red",
+            )
+            return
+
+        script = importlib.resources.files("llama_stack") / "distribution/start_conda_env.sh"
+        run_args = [
+            script,
+            image_name,
+        ]
+    else:
+        # else must be venv since that is the only valid option left.
+        current_venv = os.environ.get("VIRTUAL_ENV")
+        venv = image_name or current_venv
+        script = importlib.resources.files("llama_stack") / "distribution/start_venv.sh"
+        run_args = [
+            script,
+            venv,
+        ]
+    return run_args
+
 
 def run_with_pty(command):
     if sys.platform.startswith("win"):