Add an "Update" value element on Custom Metadata function for Contact/Lead Matching

[jimhubert]

The way the custom metadata for Contact/Lead Matching is to only add these values to new record on a new create . If we wanted to allow the matched record to also have these field values be changed we could add an "Update" value element on the Custom Metadata and code that looks for this value to be true to run this logic.

Note that @rdblake21 asked about this based on various use cases for Leads as well as the auto convert process in testing a separate pull request, so if there are questions he can help us flesh this requirement out more.