(#18577) Extend Hiera to support Proper Yaml Syntax

This patch extends the yaml backend for hiera (and thus puppet ;)
such that key/values in this syntax;

  nginx::sendfile: on
  nginx::worker_connections: 10
  nginx::gzip: on
  nginx::tcp_nopush: on

Can now be specified in Yaml syntax, Eg;

  nginx:
    worker_connections: 10
    sendfile: on
    tcp_nopush: on
    keepalive_timeout: 0