Add Contract interface for airport lookup functionality (#365)

* Add Contract interface for airport lookup functionality

* style ci fixes

app/Contracts/AirportLookup.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace App\Contracts;
+
+use App\Models\Airport;
+
+abstract class AirportLookup
+{
+    /**
+     * Lookup the information for an airport. Needs to return an instance of the
+     * Airport model, or an array with the properties listed in the Airport model.
+     *
+     * The in-use implementation can be changed in the config/phpvms.php file, so
+     * different services can be used, in-case vaCentral one isn't working or there
+     * is a better one available. Don't handle any caching in this layer, that happens
+     * at the service layer
+     *
+     * Return null if there's an error or nothing was found
+     *
+     * @example App\Services\AirportLookup\VaCentralLookup
+     *
+     * @param string $icao
+     *
+     * @return Airport|null
+     */
+    abstract public function getAirport($icao);
+}