[reports][templates] Moved URL creation outside of template

beat/web/reports/templates/reports/report_about_to_expire_email.txt

@@ -3,7 +3,7 @@ Hello,
 We'd like you to know that your report {{ report.name }}
 is still locked and about to expire.
 
-More details: http://{{ site.domain }}{{ report.get_author_absolute_url }}
+More details: {{ report_link }}
 
 Notice that, if you don't take any action to set it to public, this
 report will be set to editable mode on {{ report.expiration_date }}.