Restrict one resource with a specific role for a project

Summary:

How to restrict one resource with a specific role for a project. Ex. restrict to having only 1 resource with Project Manager role on 1 project.

Content (required):

For some project roles, we need to have only 1 resource for each of these roles. Like Project Manager, and some other custom project roles, the business need is to have only 1 person with this role on the same project.

For Project Manager, we know that we have Primary flag and we can have only one primary project manager. We need either the same for other custom roles or the possibility to not allow to add additional resources with the same project role if one resource already exists.