Addressed user detail harvesting issue

Addressed user detail harvesting issue

Altered access & usage of the /search/users/select endpoint with the
following changes:
- Removed searching of email address to prevent email detail discovery
  via hunting via search queries.
- Required the user to be logged in and have permission to manage users
  or manage permissions on items in some way.
- Removed the user migration option on user delete unless they have
  permission to manage users.

For #3108
Reported in https://huntr.dev/bounties/135f2d7d-ab0b-4351-99b9-889efac46fca/
Reported by @haxatron