Adds filtering of the `users` GraphQL field to return only human users
and only active users, through new optional `active: BOOLEAN` and
`human: BOOLEAN` arguments.

When the arguments are not provided the field will return the same users
as it does currently.

`UsersFinder` has been updated to allow scoping only human users.

This work is to allows returning only active human users within a
user mapping search.

https://gitlab.com/gitlab-org/gitlab/-/issues/471933

Changelog: added