Add Radio Callsign To Airlines (#1475)

Adds a new db field for radio telephony callsign for airlines.

Also adds necessary field to admin template.

app/Database/migrations/2022_08_20_213507_add_callsign_to_airlines.php

@@ -0,0 +1,14 @@
+<?php
+
+use App\Contracts\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class() extends Migration {
+    public function up()
+    {
+        Schema::table('airlines', function (Blueprint $table) {
+            $table->string('callsign')->nullable()->after('name');
+        });
+    }
+};