[Feature] Unify REST API response format for server,pd and store modules

### Feature Description (功能描述)

Currently, the REST API responses in the server,pd and store modules lack a standardized format.

When a request fails (e.g., Raft group not found, store heartbeat timeout), the error message is often missing or buried in logs rather than being returned in a clear, actionable format to the user.

An example response format is as follows
```json
{
"code": 200,
"message": "success", // hint for user
"data": { ... },
"status": "OK"
}
```