### Summary

The [list of builtin modules](https://docs.ansible.com/ansible/latest/collections/ansible/builtin/index.html) shows two modules with similar names and identical descriptions:

> [systemd module](https://docs.ansible.com/ansible/latest/collections/ansible/builtin/systemd_module.html#ansible-collections-ansible-builtin-systemd-module) – Manage systemd units
> [systemd_service module](https://docs.ansible.com/ansible/latest/collections/ansible/builtin/systemd_service_module.html#ansible-collections-ansible-builtin-systemd-service-module) – Manage systemd units

My guess was that `systemd_service` would manage services running with systemd, and `systemd` would manage `systemd` itself. But the description is identical. The synopsis is identical. The arguments and examples appear identical.

As a user, I expect that if one module has two names, the documentation would state that one is an alias.

Looking at [the code](https://github.com/ansible/ansible/blob/devel/lib/ansible/modules/systemd.py) I see that `systemd` is symlinked to `systemd_service.py`.

Please modify the documentation to state that one is an alias of the other, and they are identical.


### Issue Type

Documentation Report

### Component Name

systemd_service

### Ansible Version

```console
N/A
```


### Configuration

```console
N/A
```


### OS / Environment

N/A

### Additional Information

For context, my objective is to create a service file, and then enable+start it. I was hoping that there would be one module to do that. But then I saw there are two similar ones, and I thought one would create the .service file, and the other would load+run it. But that doesn't appear to be the case either.

### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
if 'ActiveState' in result['status']:
                action = None
                if module.params['state'] == 'started':
                    if not is_running_service(result['status']):
                        action = 'start'
                elif module.params['state'] == 'stopped':
                    if is_running_service(result['status']) or is_deactivating_service(result['status']):
                        action = 'stop'
                else:
                    if not is_running_service(result['status']):
                        action = 'start'
                    else:
                        action = module.params['state'][:-2]  
                    result['state'] = 'started'
                if action:
                    result['changed'] = True
                    if not module.check_mode:
                        (rc, out, err) = module.run_command("%s %s '%s'" % (systemctl, action, unit))
                        if rc != 0:
                            module.fail_json(msg="Unable to %s service %s: %s" % (action, unit, err))
            
            elif is_chroot(module) or os.environ.get('SYSTEMD_OFFLINE') == '1':
                module.warn("Target is a chroot or systemd is offline. This can lead to false positives or prevent the init system tools from working.")
            else:
                
                module.fail_json(msg="Service is in unknown state", status=result['status'])
    module.exit_json(**result)
if __name__ == '__main__':
    main()