feat: added aliases to the FROM command

Author: gplanchat

src/Dockerfile/From.php

@@ -6,12 +6,18 @@
 
 final readonly class From implements LayerInterface, \Stringable
 {
-    public function __construct(private string $source)
-    {
+    public function __construct(
+        private string $source,
+        private ?string $alias = null,
+    ) {
     }
 
     public function __toString(): string
     {
-        return sprintf('FROM %s', $this->source);
+        if ($this->alias === null) {
+            return sprintf('FROM %s', $this->source);
+        }
+
+        return sprintf('FROM %s AS %s', $this->source, $this->alias);
     }
 }