HPCC-11764 Dafilesrv authentication and encryption on transport

Current dafilesrv uses unencrypted sockets which is not secure. This update
adds a new section to the environment.conf file to optionally specify that
dafilesrv and its clients should use SSL, and points to the cert file, key file
and provides an encrypted passphrase. If specified, dafilesrv and its clients
will enable secure sockets (openSSL) and communicate in a secure manner.

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>
Should we do avail_read() here ?  avail_read will do an ioctl(FIONREAD) but wouldn't that return raw bytes ?  Which would mean an SSL_Read() might still block ??  (I am not sure)