feat: Migrating Travel_Concierge to contrib/ recipe

contrib/python/travel-concierge/.env.example

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+# Choose Model Backend: 0 -> ML Dev, 1 -> Vertex
+GOOGLE_GENAI_USE_VERTEXAI=YOUR_VALUE_HERE
+# ML Dev backend config, ignore if using Vertex.
+GOOGLE_API_KEY=YOUR_VALUE_HERE
+
+# Model Selection - Gemini 3.6 Flash is the default, but you can specify any available model.
+GOOGLE_GENAI_MODEL=gemini-3.6-flash
+
+# Vertex backend config
+GOOGLE_CLOUD_PROJECT=YOUR_VALUE_HERE
+GOOGLE_CLOUD_LOCATION=global # For certain models like 3.6 flash it must be "global".
+
+# Maps API
+GOOGLE_MAPS_API_KEY=YOUR_API_KEY_HERE
+
+# GCS Storage Bucket name - for Agent Engine deployment test
+GOOGLE_CLOUD_STORAGE_BUCKET=YOUR_BUCKET_NAME_HERE
+GOOGLE_DEPLOY_REGION=YOUR_REGION_HERE
+
+# Sample Scenario Path - Default is an empty itinerary
+# This will be loaded upon first user interaction.
+#
+# Uncomment one of the two, or create your own.
+#
+# TRAVEL_CONCIERGE_SCENARIO=travel_concierge/profiles/itinerary_seattle_example.json
+TRAVEL_CONCIERGE_SCENARIO=travel_concierge/profiles/itinerary_empty_default.json
+
+# (Optional) Arize Keys for Tracing
+ARIZE_SPACE_ID=YOUR_ARIZE_SPACE_ID_HERE
+ARIZE_API_KEY=YOUR_ARIZE_API_KEY_HERE
+
+# Environment variables extracted by extract-python-environment-variables
+ARIZE_PROJECT_NAME=adk-travel-concierge  # extracted-by:extract-env-vars; from getenv in travel_concierge/tracing.py