[1.8.x] Fixed #25121 -- Added a warning that filtering sensitive information from error reporting isn't bulletproof

Backport of 84bc4f6cdd from master

docs/howto/error-reporting.txt

@@ -114,6 +114,14 @@ and override its methods.
 Filtering error reports
 -----------------------
 
+.. warning::
+
+    Filtering sensitive data is a hard problem, and it's nearly impossible to
+    guarantee that sensitive won't leak into an error report. Therefore, error
+    reports should only be available to trusted team members and you should
+    avoid transmitting error reports unencrypted over the Internet (such as
+    through email).
+
 Filtering sensitive information
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~