HPCC-8628 Add new ESP support for MD5 authentication

Added new "htpasswd" style authentication. When admin chooses htpasswd,
this new code will manage authentication by comparing the user's
credentials with that stored in a specified htpasswd generated file

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>