Add SearXNG search provider app

SearXNG is a privacy-respecting, self-hosted metasearch engine and
an actively maintained fork of Searx. This implements the SearchInterface
to allow users to use their SearXNG instance as a search provider.

Author: jaycollett

SearXNG/SearXNG.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace App\SupportedApps\SearXNG;
+
+class SearXNG extends \App\SupportedApps implements \App\SearchInterface
+{
+    public $type = "external";
+
+    public function getResults($query, $provider)
+    {
+        $url = rtrim($provider->url, "/");
+        $q = urlencode($query);
+        return redirect($url . "/search?q=" . $q);
+    }
+}

SearXNG/app.json

@@ -0,0 +1,10 @@
+{
+  "appid": "7e356dd50dd3723072ce97822610c792f30c8d00",
+  "name": "SearXNG",
+  "website": "https://docs.searxng.org",
+  "license": "AGPL-3.0",
+  "description": "A free internet metasearch engine which aggregates results from more than 70 search services. SearXNG is a fork of Searx with continued active development.",
+  "enhanced": false,
+  "tile_background": "dark",
+  "icon": "searxng.png"
+}