Introduce ServiceDescriptor and MethodDescriptor

[aseovic]

We need to refactor builder API to use ServiceDescriptor and MethodDescriptor, which should capture all relevant information necessary to fully configure each service method.

ServiceDescriptor

• service name
• method descriptors
• interceptors that should be applied to all service methods
• default metrics configuration
• health check handler
• service-level security configuration

MethodDescriptor

• method name
• handler
• method-level interceptors
• metrics configuration override
• method-level security configuration