server: add configuration for install notifications (#4331)

* server: track `installed_at`, only send install notification on first install
* server: add configuration for install notifications

database/migrations/2022_08_16_230204_add_installed_at_column_to_servers_table.php

@@ -0,0 +1,32 @@
+<?php
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+class AddInstalledAtColumnToServersTable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::table('servers', function (Blueprint $table) {
+            $table->timestamp('installed_at')->nullable();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Schema::table('servers', function (Blueprint $table) {
+            $table->dropColumn('installed_at');
+        });
+    }
+}