Credit related to skip_on_empty_multiple

Problem/Motivation

The migrate_plus issue queue has an issue related to a version of skip_on_empty that works on multiple values.

#3054494: Alternative solution to skip_on_empty_multiple plugin from 2905929

That issue was closed per #3263852: [policy] Conditions plugins in Migrate Plus. This issue exists to give credit to any contributors that worked on that issue.

I also chose to credit everyone who contributed to the related core issue referenced in the migrate_plus issue: #2905929: Better document how skip_on_empty works with multiple value sources

That was recently closed, but there was lots of good work and discussion on that thread.

The skip_on_condition process plugin from Migrate Conditions can be used as a stand-in for this as described in the docs.

Thanks all!