Implement ticket links and blocker state

app/Models/TicketLink.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Models;
+
+use Database\Factories\TicketLinkFactory;
+use Illuminate\Database\Eloquent\Attributes\Fillable;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+#[Fillable(['source_ticket_id', 'target_ticket_id', 'ticket_link_type_id'])]
+class TicketLink extends Model
+{
+    /** @use HasFactory<TicketLinkFactory> */
+    use HasFactory;
+
+    public function sourceTicket(): BelongsTo
+    {
+        return $this->belongsTo(Ticket::class, 'source_ticket_id');
+    }
+
+    public function targetTicket(): BelongsTo
+    {
+        return $this->belongsTo(Ticket::class, 'target_ticket_id');
+    }
+
+    public function ticketLinkType(): BelongsTo
+    {
+        return $this->belongsTo(TicketLinkType::class);
+    }
+}