feat(notification): 新增 PushPlusPlus 通知支持

- 在 notification.js 中添加 PushPlusPlus 通知提供商
- 在 NotificationDialog.vue 中添加 PushPlusPlus 选项
- 在 notifications/index.js 中导入并注册 PushPlusPlus 组件

server/notification-providers/pushplusplus.js

@@ -0,0 +1,42 @@
+const NotificationProvider = require("./notification-provider");
+const axios = require("axios");
+const { DOWN, UP } = require("../../src/util");
+
+class PushPlusPlus extends NotificationProvider {
+    name = "PushPlusPlus";
+
+    async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {
+        const okMsg = "Sent Successfully.";
+        const url = `https://pushplus.plus/send`;
+        try {
+            await axios.post(notification.pushPlusPlusToken, {
+                "title": this.checkStatus(heartbeatJSON, monitorJSON),
+                "content": msg,
+            });
+
+            return okMsg;
+
+        } catch (error) {
+            this.throwGeneralAxiosError(error);
+        }
+    }
+
+    /**
+     * Get the formatted title for message
+     * @param {?object} heartbeatJSON Heartbeat details (For Up/Down only)
+     * @param {?object} monitorJSON Monitor details (For Up/Down only)
+     * @returns {string} Formatted title
+     */
+    checkStatus(heartbeatJSON, monitorJSON) {
+        let title = "UptimeKuma Message";
+        if (heartbeatJSON != null && heartbeatJSON["status"] === UP) {
+            title = "UptimeKuma Monitor Up " + monitorJSON["name"];
+        }
+        if (heartbeatJSON != null && heartbeatJSON["status"] === DOWN) {
+            title = "UptimeKuma Monitor Down " + monitorJSON["name"];
+        }
+        return title;
+    }
+}
+
+module.exports = PushPlusPlus;