feat: add invite notification emails, functionality to admin dashboard and sign up page

Signed-off-by: Miguel Nogueira <me@nogueira.codes>

app/Mail/InviteApprovedMail.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace App\Mail;
+
+use App\Invitation;
+use Illuminate\Bus\Queueable;
+use Illuminate\Mail\Mailable;
+use Illuminate\Mail\Mailables\Content;
+use Illuminate\Mail\Mailables\Envelope;
+use Illuminate\Mail\Mailables\Address;
+use Illuminate\Queue\SerializesModels;
+
+class InviteApprovedMail extends Mailable
+{
+    use Queueable, SerializesModels;
+
+    public function __construct(
+        public Invitation $invitation
+    ) {}
+
+    public function envelope(): Envelope
+    {
+        return new Envelope(
+            subject: 'Your invite for ' . config('app.name') . 'has just been approved',
+        );
+    }
+
+    public function content(): Content
+    {
+        return new Content(
+            view: 'mail.invite-approved',
+            with: [
+                'token' => $this->invitation->invitation_code,
+                'invitedDaysSince' => $this->invitation->created_at->diffInDays(now())
+            ]
+        );
+    }
+
+    public function attachments(): array
+    {
+        return [];
+    }
+}