Add logOnError option to ErrorReportValve

[Junuu]

This PR adds a new logOnError option to ErrorReportValve.

When enabled, ErrorReportValve logs request information together with the
associated Throwable when generating an error page. This makes it easier
to trace the cause of errors that result in container-generated error pages.

The logOnError option is disabled by default to preserve the existing behavior
and avoid unexpected increases in log volume.

Changes included:

• Add the logOnError attribute to ErrorReportValve
• Log error details when an error page is generated and logOnError is enabled
• Update valve.xml to document the new configuration option

This change is fully backward-compatible when logOnError is not enabled.