HPCC-10308 Add support for getting ESP files directory listing

URL Formats are:

http://ip:port/esp/files/dirpath
http://ip:port/esp/files/dirpath?format=xml
http://ip:port/esp/files/dirpath?format=json

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
HPCC-10308 Check for paths that may access directories outside esp/files

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #6325 from afishbeck/espdirectory

HPCC-10308 Add support for getting ESP files directory listing

Reviewed-By: Gordon Smith <gordon.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>