Add a config action to add to an array of configuration

Problem/Motivation

We currently have the simpleConfigUpdate config action which works well for setting a configuration value. However, in some cases, we don't want to overwrite an entire config value, we only want to add a new value, e.g. with mapping and sequence data types.

Proposed resolution

Add a new config action, simpleConfigAdd that appends a value to the end of the mapping / sequence data type.