Warn against S3 global endpoint usage

Add warning to S3 configuration documentation advising users to avoid
using s3.amazonaws.com as the --endpoint-url parameter value to prevent
PermanentRedirect errors and configuration confusion.

This addresses user issues where setting the global S3 endpoint as a
custom endpoint URL causes redirect loops and unexpected behavior.

Addresses aws#9479

Author: adev-code

awscli/topics/s3-config.rst

@@ -15,6 +15,11 @@ are provided in the case where you need to modify one of these values, either
 for performance reasons or to account for the specific environment where these
 ``aws s3`` commands are being run.
 
+.. warning::
+   S3 commands have a parameter ``--endpoint-url`` that overrides the command's
+   default URL with the given URL. Avoid using the S3 Global Endpoint
+   (s3.amazonaws.com) as the value for this parameter to prevent redirect
+   issues and other unintended behavior or errors from S3.
 
 Configuration Values
 ====================