TS-3027: add hashed intermediate certificate support

if ssl_ca_name= is configured in ssl_multicert.config
  use that to build the cert chain
else if proxy.config.ssl.CA.cert.filename is configured (along with proxy.config.ssl.CA.cert.path)
  use that file to build the chain
else if proxy.config.ssl.CA.cert.path is configured (and proxy.config.ssl.CA.cert.filename is NULL)
  use the hashed symlinks in that directory to build the chain
else
  error out because we don't have the right configuration to build the chain
Add TS-3027 to CHANGES