[FIX] web: margin-top on top of report

The margin-top/margin-bottom on a address on the top of the report does
not work because:

- display flex on an address in wkhtmltopdf is not perfectly implemented
  and seems to remove vertical margin
- margin-top on the page first visible element is removed

To fix this issue, this code remove the display:flex on the address
widget and add an empty "visible" element at the start of pages.

opw-1925894
closes #31184

addons/web/static/src/scss/report.scss

@@ -30,6 +30,18 @@ body {
     page-break-inside: avoid;
 }
 
+/* Avoid flex removing vertical margin */
+div.address.row {
+    display: block;
+}
+
+/* margin-top does not work on first visible element of page */
+body > *:first-child::before {
+    content: '\00a0';
+    display: block;
+    height: 1px;
+}
+
 /* Wkhtmltopdf doesn't support very well the media-print CSS (depends on the version) */
 .d-print-none{
     display: none;