feat: Add Discord alert webhook, ContactCategory enum, form request

- Added Discord alert webhook URL to .env.example
- Created ContactCategory enum with humanReadable method
- Implemented ContactSubmissionRequest form request
- Added ContactSubmission model with fillable and casts properties
- Included configurations for Discord alerts and honeypot protection

config/discord-alerts.php

@@ -0,0 +1,16 @@
+<?php
+
+return [
+    /*
+     * The webhook URLs that we'll use to send a message to Discord.
+     */
+    'webhook_urls' => [
+        'default' => env('DISCORD_ALERT_WEBHOOK'),
+    ],
+
+    /*
+     * This job will send the message to Discord. You can extend this
+     * job to set timeouts, retries, etc...
+     */
+    'job' => Spatie\DiscordAlerts\Jobs\SendToDiscordChannelJob::class,
+];