feat: Add a "manual" (static/fixed) monitor (#5897)

Co-authored-by: Maksim Kachynski <max.kachinsky@rocketdata.io>
Co-authored-by: Frank Elsinga <frank@elsinga.de>

server/monitor-types/manual.js

@@ -0,0 +1,36 @@
+const { MonitorType } = require("./monitor-type");
+const { UP, DOWN, PENDING } = require("../../src/util");
+
+class ManualMonitorType extends MonitorType {
+    name = "Manual";
+    type = "manual";
+    description = "A monitor that allows manual control of the status";
+    supportsConditions = false;
+    conditionVariables = [];
+
+    /**
+     * @inheritdoc
+     */
+    async check(monitor, heartbeat) {
+        if (monitor.manual_status !== null) {
+            heartbeat.status = monitor.manual_status;
+            switch (monitor.manual_status) {
+                case UP:
+                    heartbeat.msg = "Up";
+                    break;
+                case DOWN:
+                    heartbeat.msg = "Down";
+                    break;
+                default:
+                    heartbeat.msg = "Pending";
+            }
+        } else {
+            heartbeat.status = PENDING;
+            heartbeat.msg = "Manual monitoring - No status set";
+        }
+    }
+}
+
+module.exports = {
+    ManualMonitorType
+};