Add ability to bypass role delegation via alter hook

Problem/Motivation

Allow bypassing the role delegation for deletion.

For example, if your site has roles that are synced from an external tool
and therefore not manageable by the current user, but you still want
them to be able to delete the user.

Steps to reproduce

User is unable to delete if they cannot delegate all the roles the user has (which is correct in most scenarios).

Proposed resolution

Ensure that the user still has delete users permission.

Check role delegation access OR change to bypass role delegation via alter hook.

Remaining tasks

Add alter hook

User interface changes

None

API changes

.api.php doc added for documenting the alter hook

Data model changes

None