feature: enable agent update

[tschaefer]

No description provided.

[Copilot]

Pull request overview

This PR adds the ability to update existing agents in the system by implementing an UpdateAgent RPC endpoint that allows modification of agent configuration fields such as labels, log sources, metrics settings, and profiles.

Key Changes:

• Added UpdateAgent RPC method to the AgentService proto definition
• Implemented UpdateAgent handlers across the gRPC server, controller, and model layers
• Generated corresponding protobuf code for the new UpdateAgentRequest and UpdateAgentResponse messages

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
api/api.proto	Defines the UpdateAgent RPC method and its request/response message structures
api/api.pb.go	Generated protobuf code for UpdateAgentRequest and UpdateAgentResponse message types
api/api_grpc.pb.go	Generated gRPC client and server code for the UpdateAgent RPC method
internal/grpc/server.go	Implements the UpdateAgent gRPC handler with request validation and error handling
internal/controller/agent.go	Implements the UpdateAgent business logic including agent retrieval, field updates, and persistence
internal/model/agent.go	Implements the UpdateAgent database operation using GORM's Save method

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