### 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
unit_search = '{unit_base}{sep}'.format(unit_base=unit_base, sep=sep)
            (rc, out, err) = module.run_command("{systemctl} list-unit-files '{unit_search}*'".format(systemctl=systemctl, unit_search=unit_search))
            is_systemd = unit_search in out
            (rc, out, err) = module.run_command("{systemctl} is-active '{unit}'".format(systemctl=systemctl, unit=unit))
            result['status']['ActiveState'] = out.rstrip('\n')
        else:
            
            valid_enabled_states = [
                "enabled",
                "enabled-runtime",
                "linked",
                "linked-runtime",
                "masked",
                "masked-runtime",
                "static",
                "indirect",
                "disabled",
                "generated",
                "transient"]
            (rc, out, err) = module.run_command("%s is-enabled '%s'" % (systemctl, unit))
            if out.strip() in valid_enabled_states:
                is_systemd = True
            else:
                
                
                (rc, out, err) = module.run_command("%s list-unit-files '%s'" % (systemctl, unit))
                if rc == 0:
                    is_systemd = True
                else: