feat: autoplace fields from placeholders (#2111)

This PR introduces automatic detection and placement of fields and
recipients based on PDF placeholders.

The placeholders have the following structure:
- `{{fieldType,recipientPosition,fieldMeta}}` 
- `{{text,r1,required=true,textAlign=right,fontSize=50}}`

When the user uploads a PDF document containing such placeholders, they
get converted automatically to Documenso fields and assigned to
recipients.

apps/documentation/pages/users/documents/_meta.js

@@ -3,6 +3,7 @@ export default {
   'document-preferences': 'Document Preferences',
   'document-visibility': 'Document Visibility',
   fields: 'Document Fields',
+  'pdf-placeholders': 'PDF Placeholders',
   'email-preferences': 'Email Preferences',
   'ai-detection': 'AI Recipient & Field Detection',
   'default-recipients': 'Default Recipients',