Add declarative agent models and factory abstractions

[markwallace-microsoft]

• Add support to load any type of agent from a YAML declarative representation
• Create samples that show various permutations, including tool configuration
• Use PowerFX to evaluate values
• Add support for all Foundry Agent tool types
• Complete all TODO's
• 80% unit test coverage and integration tests
• Use code generation dotnet/src/Microsoft.Agents.AI.Declarative/Extensions/PropertyInfoExtensions.cs
• Add documentation to the sample templates
• Add template samples showing all connection types
• Use Dictionary in place of IConfiguration
• Move XXXExpressionExtensions into internal helpers

[matthewmeyer]

I would love to see this feature, the AutoGen Python component model and seralization and deseralization support are a really powerful tool and could help drive parity between the language specific implementations.