Add filtering active and human users in GraphQL

Adds filtering of the `users` GraphQL field to by human users
and 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 humans `humans: true`
- Scoping non-humans `without_humans: true`
- Scoping non-active users `without_active: true`

`/users` REST API endpoint has been updated to support the new users
finder params.

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