Provide a way to encrypt users if module is enabled via config import

Problem/Motivation

After #3257640: Respect is_syncing in hook_install → , if the module is enabled via config import the user emails will remain unencrypted in the database. The reason for disabling the profile encryption during configuration import is that it is not really the correct time to spend a few minutes changing the database. However, this

Steps to reproduce

Enable the module by adding the module to the core.extension.yml file. Check that users remain unencrypted.

Proposed resolution

Provide a warning on the status report that emails have not yet been encrypted. Provide a mechanism to encrypt these emails using a batch operation as it might be necessary to do this for thousands of users.