Disable master maintenance scripts when admin server runs (#8499)

* Disable master maintenance scripts when admin server runs

* Stop defaulting master maintenance scripts

* Apply suggestion from @gemini-code-assist[bot]

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Apply suggestion from @gemini-code-assist[bot]

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Clarify master scripts are disabled by default

* Skip master maintenance scripts when admin server is connected

* Restore default master maintenance scripts

* Document admin server skip for master maintenance scripts

---------

Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

weed/admin/dash/admin_presence_lock.go

@@ -0,0 +1,61 @@
+package dash
+
+import (
+	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/cluster"
+	"github.com/seaweedfs/seaweedfs/weed/wdclient"
+	"github.com/seaweedfs/seaweedfs/weed/wdclient/exclusive_locks"
+)
+
+const adminPresenceClientName = "admin-server"
+
+type adminPresenceLock struct {
+	locker *exclusive_locks.ExclusiveLocker
+	stopCh chan struct{}
+}
+
+func newAdminPresenceLock(masterClient *wdclient.MasterClient) *adminPresenceLock {
+	if masterClient == nil {
+		return nil
+	}
+	return &adminPresenceLock{
+		locker: exclusive_locks.NewExclusiveLocker(masterClient, cluster.AdminServerPresenceLockName),
+		stopCh: make(chan struct{}),
+	}
+}
+
+func (l *adminPresenceLock) Start() {
+	if l == nil || l.locker == nil {
+		return
+	}
+	l.locker.SetMessage("admin server connected")
+	go func() {
+		ticker := time.NewTicker(5 * time.Second)
+		defer ticker.Stop()
+		for {
+			if !l.locker.IsLocked() {
+				l.locker.RequestLock(adminPresenceClientName)
+			}
+			select {
+			case <-l.stopCh:
+				return
+			case <-ticker.C:
+			}
+		}
+	}()
+}
+
+func (l *adminPresenceLock) Stop() {
+	if l == nil {
+		return
+	}
+	select {
+	case <-l.stopCh:
+	default:
+		close(l.stopCh)
+	}
+	if l.locker != nil {
+		l.locker.ReleaseLock()
+	}
+}