[14.0][FIX] document_page: Stored XSS

unitary tests added

post-migration script added

document_page/migrations/14.0.1.2.4/post-migration.py

@@ -0,0 +1,9 @@
+from openupgradelib import openupgrade
+
+
+@openupgrade.migrate()
+def migrate(env, version):
+    document_page_history = env["document.page.history"]
+    for record in document_page_history.search([]):
+        # Apply default HTML sanitize by reassigning the content
+        record.content = record.content