[Plan] Discuss strategy for long term use of entity validation in the migration system

Problem/Motivation

Follow-up from #2745797: Add option to content entity destinations for validation
Relevant discussion at https://youtu.be/9rBkBl4uGlg?t=1265

Discussion on whether we can make entity validation the new default in migrations, and how we can do that.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet