Add http and https proxy feature

Added new proxy feature based on http and https proxy agents.
Proxy feature works like notifications, there is many proxy
could be related one proxy entry.

Supported features
- Proxies can activate and disable in bulk
- Proxies auto enabled by default for new monitors
- Proxies could be applied in bulk to current monitors
- Both authenticated and anonymous proxies supported
- Export and import support for proxies

server/model/proxy.js

@@ -0,0 +1,21 @@
+const { BeanModel } = require("redbean-node/dist/bean-model");
+
+class Proxy extends BeanModel {
+    toJSON() {
+        return {
+            id: this._id,
+            userId: this._user_id,
+            protocol: this._protocol,
+            host: this._host,
+            port: this._port,
+            auth: !!this._auth,
+            username: this._username,
+            password: this._password,
+            active: !!this._active,
+            default: !!this._default,
+            createdDate: this._created_date,
+        };
+    }
+}
+
+module.exports = Proxy;