### Summary

I was surprised to after using Ansible to add some users to a group, that they had been removed from all other groups (crucially, including one used to grant them `sudo` rights!).



### Issue Type

Documentation Report

### Component Name

user_module

### Ansible Version

```console
nsible [core 2.11.5]
  config file = /redacted/git/devops-ansible/ansible.cfg
  configured module search path = ['/home/mark/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.9/site-packages/ansible
  ansible collection location = /home/mark/.ansible/collections:/usr/share/ansible/collections
  executable location = /sbin/ansible
  python version = 3.9.7 (default, Aug 31 2021, 13:28:12) [GCC 11.1.0]
  jinja version = 3.0.1
  libyaml = True
```


### Configuration

```console
N/A
```


### OS / Environment

Arch Linux

### Additional Information

I re-read the docs for the `user` built-in and it only mentions that the user will be *added* to groups mentioned in the groups list. The docs currently fail to mention that they will be removed from all groups *not* in the groups array.

I presume this behavior is as intended, but the docs should clarify that the user's non-primary groups will be set to exactly those in the list, any other pre-existing group memberships will be removed.

Here's a sample playbook that illustrated the behavior:

```yaml
---
- hosts: fave-server
  become: true
  become_user: root
  tasks:
    - name: "add users to some group"
      loop:
        - sue
        - john
      user:
        name: "{{ item }}"
        state: present
        groups:
          - some
```

Try having the users already exist with other group memberships and they will be removed and replace with only a `some` group membership. (I tested with Ansible 2.11.5). 

### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
C(/Library/Preferences/com.apple.loginwindow.plist).
  - On FreeBSD, this module uses C(pw useradd) and C(chpass) to create, C(pw usermod) and C(chpass) to modify,
    C(pw userdel) remove, C(pw lock) to lock, and C(pw unlock) to unlock accounts.
  - On all other platforms, this module uses C(useradd) to create, C(usermod) to modify, and
    C(userdel) to remove accounts.
seealso:
- module: ansible.posix.authorized_key
- module: ansible.builtin.group
- module: ansible.windows.win_user
author:
- Stephen Fromm (@sfromm)
'''
EXAMPLES = r'''
- name: Add the user 'johnd' with a specific uid and a primary group of 'admin'
  ansible.builtin.user:
    name: johnd
    comment: John Doe
    uid: 1040
    group: admin
- name: Add the user 'james' with a bash shell, appending the group 'admins' and 'developers' to the user's groups
  ansible.builtin.user:
    name: james
    shell: /bin/bash
    groups: admins,developers
    append: yes
- name: Remove the user 'johnd'
  ansible.builtin.user:
    name: johnd
    state: absent
    remove: yes