Create an admin for each site in a Multi-Site Config

Account type - US
A brief description of the business - We are in IT services firm that supports small businesses as well as a government services division that does computer-based training for government entities.
A high level description of the product or feature being requested - I would like to have a feature that allows you to have a SITE ADMIN, basically, they are only able to manage the users in a particular site. We currently have a multi-site config and we want to try and segregate the management for each site, as we have dedicated staff at each site.
A typical use case scenario explaining how your business would use the feature - see #3
Benefit of such feature - See #3
Include any related case number if applicable - N/A
Number of Users and/or Digital Lines - 190

Idea