Pipelines: Add ability to split a value and convert the resulting array values

## What?

In Graylog pipelines rules, it is currently possible to split a string value into an array of values (using the `split` pipeline functions), but it is not possible to convert the individual values resulting from the array to another data type (for example, to use the `to_ip` function on each array value). Technically, array values can be accessed by index value for example `array[0] or array[1]` and converted individually, but this is not possible to use on an array of indeterminate length.

## Why?

The user would like to use this functionality to store an array of IP addresses in Elasticsearch with the native IP format type.

For example, from the value: `192.168.1.1,192.168.1.2,192.168.1.3,192.168.1.4`

HS-581667714