[FIX] l10n_generic_coa: missing values for demo data for OCR

The demo invoice for the OCR had incomplete fields to work properly, the
'Send for digitalization' button was missing and there was no attachment
preview.

closes odoo/odoo#35528

Signed-off-by: Florian Daloze (fda) <fda@odoo.com>

addons/l10n_generic_coa/data/account_invoice_demo.xml

@@ -63,14 +63,21 @@
         </record>
 
         <!-- ==== Invoice Demo 6 - Draft Vendor Bill for OCR ==== -->
+        <record id="ir_attachment_in_invoice_draft" model="ir.attachment">
+            <field name="type">binary</field>
+            <field name="datas" type="base64" file="l10n_generic_coa/static/src/demo/in_invoice_yourcompany_demo.pdf"/>
+            <field name="name">in_invoice_yourcompany_demo.pdf</field>
+            <field name="res_model">account.move</field>
+        </record>
+
         <record id="demo_invoice_extract" model="account.move" context="{'type': 'in_invoice'}">
+            <field name="type">in_invoice</field>
             <field name="invoice_user_id" ref="base.user_demo"/>
+            <field name="message_main_attachment_id" ref="ir_attachment_in_invoice_draft"/>
         </record>
 
         <record id="ir_attachment_in_invoice_draft" model="ir.attachment">
-            <field name="type">binary</field>
-            <field name="datas" type="base64" file="l10n_generic_coa/static/src/demo/in_invoice_yourcompany_demo.pdf"/>
-            <field name="name">in_invoice_yourcompany_demo.pdf</field>
+            <field name="res_id" ref="demo_invoice_extract"/>
         </record>
 
         <record id="mail_message_in_invoice_0" model="mail.message">