HPCC-8627 Add new ESP HTPASSWD style MD5 authentication

Add new roadmap item "htpasswd" authentication method that does
not involve the complexities of LDAP. It was decided to authenticate
against an HTPASSWD generated password file, located through a config
setting.

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>
Merge pull request #4013 from RussWhitehead/htPasswd

HPCC-8627 Add new ESP HTPASSWD style MD5 authentication

Reviewed-By: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>