Mark a config entity as 'syncing' during a migration update

Problem/Motivation

In ✨ Mark an entity as 'syncing' during a migration update Needs work content entities were addressed. This issue is to do the same for config entities.

The comments #36 ✨ Mark an entity as 'syncing' during a migration update Needs work - #39. It does seem that #36 questions whether this is worthwhile.

Steps to reproduce

Proposed resolution

Remaining tasks

MR
review
commit

User interface changes

API changes

Data model changes

Release notes snippet