Refactor of micropub request handling

Trying to organise the code better. It now temporarily doesn’t support
update requests. Thought the spec defines them as SHOULD features and
not MUST features. So safe for now :)

app/Services/Micropub/MicropubHandlerRegistry.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Services\Micropub;
+
+use App\Exceptions\MicropubHandlerException;
+
+class MicropubHandlerRegistry
+{
+    /**
+     * @var MicropubHandlerInterface[]
+     */
+    protected array $handlers = [];
+
+    public function register(string $type, MicropubHandlerInterface $handler): self
+    {
+        $this->handlers[$type] = $handler;
+
+        return $this;
+    }
+
+    /**
+     * @throws MicropubHandlerException
+     */
+    public function getHandler(string $type): MicropubHandlerInterface
+    {
+        if (! isset($this->handlers[$type])) {
+            throw new MicropubHandlerException("No handler registered for '{$type}'");
+        }
+
+        return $this->handlers[$type];
+    }
+}