Auth flow and ENV pattern for all samples

[axelsrz]

This pull request introduces several changes to improve the handling of anonymous authentication and environment configuration in the Microsoft Agents Builder and related test samples. The most important changes include adding support for an anonymous token provider, updating the configuration to use environment variables, and refining the anonymous authentication strategy.

Improvements to Anonymous Authentication:

• libraries/Builder/microsoft-agents-builder/microsoft/agents/builder/channel_service_adapter.py: Changed the condition to use anonymous authentication if the claims_identity.authentication_type is "Anonymous".
• libraries/Builder/microsoft-agents-builder/microsoft/agents/builder/rest_channel_service_client_factory.py: Introduced _ANONYMOUS_TOKEN_PROVIDER and updated the create_connector_client and create_user_token_client methods to use the anonymous token provider when use_anonymous is True. [1] [2] [3]
• libraries/Core/microsoft-agents-authorization/microsoft/agents/authorization/anonymous_token_provider.py: Added a new AnonymousTokenProvider class that provides an anonymous token for authentication.
• libraries/Core/microsoft-agents-authorization/microsoft/agents/authorization/jwt_token_validator.py: Added a get_anonymous_claims method to return a ClaimsIdentity with anonymous authentication.
• libraries/Hosting/microsoft-agents-hosting-aiohttp/microsoft/agents/hosting/aiohttp/jwt_authorization_middleware.py: Refined the anonymous strategy by setting request["claims_identity"] to the result of get_anonymous_claims when CLIENT_ID is not provided.

Environment Configuration Updates:

• test_samples/agent_to_agent/agent_1/app.py, test_samples/agent_to_agent/agent_2/app.py, test_samples/echo_agent/app.py: Added load_dotenv() to load environment variables from a .env file. [1] [2] [3]
• test_samples/agent_to_agent/agent_1/config.py, test_samples/agent_to_agent/agent_2/config.py, test_samples/echo_agent/config.py: Updated the configuration classes to use environment variables for TENANT_ID, CLIENT_ID, CLIENT_SECRET, and other settings. [1] [2] [3]