Command to audit all migrations

Problem/Motivation

It'd be really useful if there was a single command that could audit all available migrations (maybe filtered by group) and show how many records need to be purged.

Proposed resolution

Add command for listing all migrations and the number of records that need to be purged.
An option to filter by group or tag would be very helpful.

Remaining tasks

Write a patch/MR for this.

User interface changes

A new Drush command would be available for listing records need to be purged for each requested migration.

API changes

TBD

Data model changes

TBD