Add support for "without_project_bots" parameter in Users API

[demianh]

There seems to be a new parameter in the Users API:

Attribute	Type	Required	Description
without_project_bots	boolean	no	Filters user without project bots. Default is false.

see https://docs.gitlab.com/ee/api/users.html

It would be nice to add this parameter. Thx!

[stale]

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