Define the Diagnostics gRPC Service and the relevent message type

[lonng]

This issue is part of proposal #13481 about Diagnostics gRPC Service

Proto definition

// Diagnostics service for TiDB cluster componenets.
service Diagnostics {
	// Searchs log in the target node
	rpc search_log(SearchLogRequest) returns (SearchLogResponse) {};
	// Retrieves server info in the target node
	rpc server_info(ServerInfoRequest) returns (ServerInfoResponse) {};
}

enum LogLevel {
	Debug = 0;
	Info = 1;
	Warn = 2;
	Trace = 3;
	Critical = 4;
	Error = 5;
}

message SearchLogRequest {
	int64 start_time = 1;
	int64 end_time = 2;
	LogLevel level = 3;
	string pattern = 4;
	int64 limit = 5;
}

message SearchLogResponse {
	repeated LogMessage messages = 1;
}

message LogMessage {
	int64 time = 1;
	LogLevel level = 2;
	string message = 3;
}

enum ServerInfoType {
	All = 0;
	HardwareInfo = 1;
	SystemInfo = 2;
	LoadInfo = 3;
}

message ServerInfoRequest {
	ServerInfoType tp = 1;
}

message ServerInfoItem {
	// cpu, memory, disk, network ...
	string tp = 1;
	// eg. network: lo1/eth0, cpu: core1/core2, disk: sda1/sda2 
	string name = 2;
	string key = 3;
	string value = 4;
}

message ServerInfoResponse {
	repeated ServerInfoItem items = 1;
}

Rationale

Unifying the information obtained into the same interface and using a unified structure for the returned data types facilitates the flexibility to add new system information. If we define a separate interface for each type of system information, it will lead to the expansion of the relevant data structure.