feat: add content aliases for barcode, multi-step, and forms

- Add barcode.md stub in inputs pointing to /plugins/barcode
- Add multi-step.md stub in inputs pointing to /plugins/multi-step
- Add canonical redirect for forms.md to /inputs/form

Author: andrew-boyd

2.essentials/2.forms.md

@@ -1,4 +1,5 @@
 ---
 title: Forms
 description: Collect all of your FormKit data, submit to your server, and handle server-side error messages.
+canonical: /inputs/form
 ---

3.inputs/barcode.md

@@ -0,0 +1,7 @@
+---
+title: Barcode
+description: Scan barcodes and QR codes
+navigation:
+  plugin: true
+canonical: /plugins/barcode
+---

3.inputs/multi-step.md

@@ -0,0 +1,7 @@
+---
+title: Multi-step
+description: Easily add multi-step sections to your FormKit forms
+navigation:
+  plugin: true
+canonical: /plugins/multi-step
+---