Logstash config and the possibility of repeating the options in the plugin block

This issue or feature was originally reported by @tsouza

The current Logstash syntax parsing allows you to create this code when the plugin options are of type `array`:

```
input
{
file
{
path => "/opt/elk/data/syslogs/1.log"
path => "/opt/elk/data/syslogs/2.log"
path => "/opt/elk/data/syslogs/3.log"
path => "/opt/elk/data/syslogs/4.log"
path => "/opt/elk/data/syslogs/5.log"
path => "/opt/elk/data/syslogs/6.log"
path => "/opt/elk/data/syslogs/7.log"

}
}
```

Inside the plugin, the content of the `@path` variable will be an array containing all the different paths.

```ruby
["/opt/elk/data/syslogs/1.log" , "/opt/elk/data/syslogs/2.log" , "/opt/elk/data/syslogs/3.log" , "/opt/elk/data/syslogs/4.log" , "/opt/elk/data/syslogs/5.log" , "/opt/elk/data/syslogs/6.log" , "/opt/elk/data/syslogs/7.log"
```

After discussing with @andrewvc we know that new `LIR` feature doesn't support that use case and we think we should not support that syntax going forward in 6.0.
I do not believe that we ever exposed that syntax in our documentation and this could create other problems if we ever want to support another format like JSON or YAML.

Also, it feels like a hack since in our documentation we never mention that you can use multiple time the same plugin option.

Thoughts on not supporting and deprecating that syntax?