[Feat]: Inspection of gRPC A2A agents

### Is your feature request related to a problem? Please describe.

The inspector expects JSON-RPC agent. I doesn't work with a gRPC A2A agent.

Error: An internal server error occurred: HTTP Error 503: Network communication error fetching agent card from http://localhost:50051/.well-known/agent.json: illegal request line

This error is due to the fact that my agent is not exposing an HTTP endpoint for the card, but it expects to receive GetAgentCard gRPC call.

### Describe the solution you'd like

Extend the inspector to inspect gRPC A2A agents

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

The inspector currently fetches an agent card via HTTP from /.well-known/agent.json. For gRPC A2A agents, it needs to make a GetAgentCard gRPC call instead. Start by examining the existing HTTP-based inspection logic, then understand the gRPC service definition for A2A agents. Implementing this requires adding gRPC client support and handling both transport types. 'Done' means the inspector can successfully retrieve and display the card from a gRPC agent without the 503 error.

Scritto dal modello di indicizzazione a partire dal testo della issue.