Add extra_args parameter for passing extra arguments to mon-put-instance-data.pl

[cliffano]

We have a use case where we need to pass additional args to mon-put-instance-data.pl script, hence we're introducing a new extra_args parameter as part of this PR.

Example usage:

  class { '::cloudwatch':
      enable_mem_util         => true,
      enable_mem_used         => true,
      enable_mem_avail        => true,
      enable_disk_space_util  => true,
      enable_disk_space_used  => true,
      enable_disk_space_avail => true,
      enable_swap_util        => false,
      enable_swap_used        => false,
      auto_scaling            => $autoscaling,
      cron_min                => '*',
      disk_path               => $disk_path ,
      zip_url                 => 'https://somesite.com/our-custom-aws-scripts-mon-1.3.0.zip',
      extra_args              => '--proxy=http://some-proxy:3128'
    }