Issue #3383175 by spryah: add error pattern

Closes #3383175

templates/patterns/error/error.ui_patterns.yml

+error:
+  label: Error
+  description: "Error page content (404/403)"
+  settings:
+    pictogram:
+      type: select
+      label: Pictogram
+      options:
+        technical-error: Technical error (404)
+        padlock: Forbidden (403)
+      default_value: technical-error
+  fields:
+    title:
+      type: text
+      label: Title
+      description: Page title.
+      preview: "Page not found"
+    error_name:
+      type: text
+      label: Error name
+      preview: "404 error"
+    teaser:
+      type: text
+      label: Teaser
+      description: Short explanation.
+      preview: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Etiam eu turpis molestie, dictum est a, mattis tellus. Sed dignissim, metus nec fringilla accumsan, risus sem sollicitudin lacus, ut interdum tellus elit sed risus. Maecenas eget condimentum velit, sit amet feugiat lectus."
+    text:
+      type: text
+      label: Text
+      description: Detailed text.
+      preview: "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Etiam eu turpis molestie, dictum est a, mattis tellus. Sed dignissim, metus nec fringilla accumsan, risus sem sollicitudin lacus, ut interdum tellus elit sed risus. Maecenas eget condimentum velit, sit amet feugiat lectus."
+    content:
+      type: render
+      label: Content
+      description: Usually a list of links/buttons to help the user find their way.
+      preview:
+        type: pattern
+        id: button_group
+        settings:
+          inline_from: sm
+        fields:
+          buttons:
+            - type: pattern
+              id: button
+              fields:
+                label: Homepage
+                url: "/"
+            - type: pattern
+              id: button
+              variant: secondary
+              fields:
+                label: Contact us
+                url: "https://example.com"