Add scheduled tasks (#13470)

### What problem does this PR solve?

1. RAGFlow server will send heartbeat periodically.
2. This PR will including:
- Scheduled task
- API server message sending
- Admin server API to receive the message.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/common/status_message.go

@@ -0,0 +1,33 @@
+package common
+
+import (
+	"time"
+)
+
+type MessageType string
+
+const (
+	MessageHeartbeat MessageType = "heartbeat"
+	MessageMetric    MessageType = "metric"
+	MessageEvent     MessageType = "event"
+)
+
+type ServerType string
+
+const (
+	ServerTypeAPI       ServerType = "api_server"     // API server
+	ServerTypeWorker    ServerType = "ingestor"       // Ingestion server
+	ServerTypeScheduler ServerType = "data_collector" // Data collection server
+)
+
+type BaseMessage struct {
+	MessageID   int64                  `json:"report_id"`
+	MessageType MessageType            `json:"report_type"`
+	ServerName  string                 `json:"server_id"`
+	ServerType  ServerType             `json:"server_type"`
+	Host        string                 `json:"host"`
+	Port        int                    `json:"port"`
+	Version     string                 `json:"version"`
+	Timestamp   time.Time              `json:"timestamp"`
+	Ext         map[string]interface{} `json:"ext,omitempty"`
+}