[FIX] pos: allow new line in receipt header

To reproduce the error:
1. In the settings of a POS, enable "Header & Footer"
2. Add a header (with at least one line break)
4. Start a session
4. Validate an order

Error: The header of the receipt is incorrect, line breaks are not
applied

OPW-2528558

addons/point_of_sale/static/src/xml/Screens/ReceiptScreen/OrderReceipt.xml

@@ -33,7 +33,7 @@
                     <t t-raw="receipt.header_html" />
                 </t>
                 <t t-if="!receipt.header_html and receipt.header">
-                    <div><t t-esc="receipt.header" /></div>
+                    <div style="white-space:pre-line"><t t-esc="receipt.header" /></div>
                 </t>
                 <t t-if="receipt.cashier">
                     <div class="cashier">