Multiple outputs from Mapping Table

## Background
Sometimes you might need 2 columns from the mapping table in your dataset.

## Feature
Allow Mapping Table CR to have an output of more than one column

## Example [Optional]
Mapping on ClientID column, wanting to take away name and surname from the MappingTable.

## Proposed Solution [Optional]
```scala
case class MappingConformanceRule(
order: Int,
controlCheckpoint: Boolean,
mappingTable: String,
mappingTableVersion: Int,
attributeMappings: Map[String, String], //key = mapping table column, value = input df column
targetAttribute: Array[String], // <----
outputColumn: Array[String], // <----
isNullSafe: Boolean = false) extends ConformanceRule
```

## Question
Would other rules benefit from this?