add a $pg_hba_conf_template parameter to the class postgresql::config to...

... allow the default pg_hba.conf template to be overrideen

example usage:

  class { 'postgresql::server':
    config_hash => {
      'pg_hba_conf_template'       => 'mymodule/pg_hba.conf.erb',
    },
  }

Per discussion in https://github.com/puppetlabs/puppet-postgresql/pull/72