Python: docs: add env example files for durabletask samples

python/samples/04-hosting/durabletask/01_single_agent/.env.example

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+# Azure AI Foundry project endpoint URL, e.g. https://your-project.services.ai.azure.com/api/projects/your-project
+FOUNDRY_PROJECT_ENDPOINT=
+
+# Model deployment name in your Foundry project
+FOUNDRY_MODEL=

python/samples/04-hosting/durabletask/02_multi_agent/.env.example

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+# Azure OpenAI resource endpoint URL, e.g. https://your-resource.openai.azure.com/
+AZURE_OPENAI_ENDPOINT=
+
+# Azure OpenAI model deployment name
+AZURE_OPENAI_MODEL=

python/samples/04-hosting/durabletask/03_single_agent_streaming/.env.example

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+# Azure AI Foundry project endpoint URL, e.g. https://your-project.services.ai.azure.com/api/projects/your-project
+FOUNDRY_PROJECT_ENDPOINT=
+
+# Model deployment name in your Foundry project
+FOUNDRY_MODEL=
+
+# Redis connection string (defaults to redis://localhost:6379 if unset)
+REDIS_CONNECTION_STRING=
+
+REDIS_STREAM_TTL_MINUTES=10  # Stream key TTL in minutes; use a positive integer (default: 10). Non-positive values remove keys immediately (Redis EXPIRE).

python/samples/04-hosting/durabletask/04_single_agent_orchestration_chaining/.env.example

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+# Azure AI Foundry project endpoint URL, e.g. https://your-project.services.ai.azure.com/api/projects/your-project
+FOUNDRY_PROJECT_ENDPOINT=
+
+# Model deployment name in your Foundry project
+FOUNDRY_MODEL=

python/samples/04-hosting/durabletask/05_multi_agent_orchestration_concurrency/.env.example

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+# Azure AI Foundry project endpoint URL, e.g. https://your-project.services.ai.azure.com/api/projects/your-project
+FOUNDRY_PROJECT_ENDPOINT=
+
+# Model deployment name in your Foundry project
+FOUNDRY_MODEL=

python/samples/04-hosting/durabletask/06_multi_agent_orchestration_conditionals/.env.example

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+# Azure OpenAI resource endpoint URL, e.g. https://your-resource.openai.azure.com/
+AZURE_OPENAI_ENDPOINT=
+
+# Azure OpenAI model deployment name
+AZURE_OPENAI_MODEL=

python/samples/04-hosting/durabletask/07_single_agent_orchestration_hitl/.env.example

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+# Azure AI Foundry project endpoint URL, e.g. https://your-project.services.ai.azure.com/api/projects/your-project
+FOUNDRY_PROJECT_ENDPOINT=
+
+# Model deployment name in your Foundry project
+FOUNDRY_MODEL=