Users/axsuarez/enable no config

[axelsrz]

This pull request introduces several improvements and refactorings to both the core hosting logic and the test sample agent, focusing on simplifying configuration, improving error handling, and making the agent sample more approachable. The most significant changes are grouped below.

Core library improvements

• The CloudAdapter constructor now allows connection_manager to be optional, defaulting to None, making it easier to instantiate in simple scenarios.
• In the AgentApplication initialization, the requirement for a Connections instance is removed if authorization is not explicitly provided. Instead, authorization options are filtered from configuration and passed directly, making setup more flexible and less error-prone.
• Added an explicit error and exception if _connection_manager is not configured when handling OAuth On-Behalf-Of (OBO) flows, improving clarity and debugging for misconfigurations.
• The JWT authorization middleware now checks if auth_config is present before accessing its properties, preventing potential runtime errors when configuration is missing or incomplete.

Test sample and server refactoring

• The emtpy_agent.py sample is significantly simplified: unnecessary imports and manual configuration steps are removed, and the agent is now initialized with just MemoryStorage and a CloudAdapter. The help and echo behaviors are streamlined, and server startup is delegated to a shared start_server utility.
• The shared server utility now adds a health check endpoint (GET /api/messages) to aid in testing and monitoring.