HPCC-11506 - Alert to contain existing files

Add name(s) of files to alert user what files are the ones that currently exist.
Add "..more.." if more than 10 files are duplicates.

Signed-off by: Miguel Vazquez <miguel.vazquez@lexisnexis.com>
Merge pull request #6433 from miguelvazq/HPCC-11506.1

HPCC-11506 - Alert to contain existing files

Reviewed-By: Gordon Smith <gordon.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>