feat: add support for running in a venv (#1018)

# What does this PR do?

add --image-type to `llama stack run`. Which takes conda, container or
venv also add start_venv.sh which start the stack using a venv

resolves #1007

## Test Plan

running locally:

`llama stack build --template ollama --image-type venv`
`llama stack run --image-type venv
~/.llama/distributions/ollama/ollama-run.yaml`
...
```
llama stack run --image-type venv ~/.llama/distributions/ollama/ollama-run.yaml
Using run configuration: /Users/charliedoern/.llama/distributions/ollama/ollama-run.yaml
+ python -m llama_stack.distribution.server.server --yaml-config /Users/charliedoern/.llama/distributions/ollama/ollama-run.yaml --port 8321
Using config file: /Users/charliedoern/.llama/distributions/ollama/ollama-run.yaml
Run configuration:
apis:
- agents
- datasetio
...
```

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

llama_stack/distribution/start_venv.sh

@@ -0,0 +1,71 @@
+#!/bin/bash
+
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+set -euo pipefail
+
+RED='\033[0;31m'
+NC='\033[0m' # No Color
+
+error_handler() {
+  echo "Error occurred in script at line: ${1}" >&2
+  exit 1
+}
+
+trap 'error_handler ${LINENO}' ERR
+
+if [ $# -lt 3 ]; then
+  echo "Usage: $0 <venv_path> <yaml_config> <port> <script_args...>"
+  exit 1
+fi
+
+venv_path="$1"
+shift
+
+yaml_config="$1"
+shift
+
+port="$1"
+shift
+
+# Initialize env_vars as an empty array
+env_vars=""
+other_args=""
+# Process environment variables from --env arguments
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+  --env)
+
+    if [[ -n "$2" ]]; then
+      env_vars="$env_vars --env $2"
+      shift 2
+    else
+      echo -e "${RED}Error: --env requires a KEY=VALUE argument${NC}" >&2
+      exit 1
+    fi
+    ;;
+  *)
+    other_args="$other_args $1"
+    shift
+    ;;
+  esac
+done
+
+# Activate virtual environment
+if [ ! -d "$venv_path" ]; then
+  echo -e "${RED}Error: Virtual environment not found at $venv_path${NC}" >&2
+  exit 1
+fi
+
+source "$venv_path/bin/activate"
+
+set -x
+python -m llama_stack.distribution.server.server \
+  --yaml-config "$yaml_config" \
+  --port "$port" \
+  $env_vars \
+  $other_args