### 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
"GuessMainPID": "yes",
            "IOScheduling": "0",
            "Id": "crond.service",
            "IgnoreOnIsolate": "no",
            "IgnoreOnSnapshot": "no",
            "IgnoreSIGPIPE": "yes",
            "InactiveEnterTimestampMonotonic": "0",
            "InactiveExitTimestamp": "Sun 2016-05-15 18:28:49 EDT",
            "InactiveExitTimestampMonotonic": "8135942",
            "JobTimeoutUSec": "0",
            "KillMode": "process",
            "KillSignal": "15",
            "LimitAS": "18446744073709551615",
            "LimitCORE": "18446744073709551615",
            "LimitCPU": "18446744073709551615",
            "LimitDATA": "18446744073709551615",
            "LimitFSIZE": "18446744073709551615",
            "LimitLOCKS": "18446744073709551615",
            "LimitMEMLOCK": "65536",
            "LimitMSGQUEUE": "819200",
            "LimitNICE": "0",
            "LimitNOFILE": "4096",
            "LimitNPROC": "3902",
            "LimitRSS": "18446744073709551615",
            "LimitRTPRIO": "0",
            "LimitRTTIME": "18446744073709551615",
            "LimitSIGPENDING": "3902",
            "LimitSTACK": "18446744073709551615",
            "LoadState": "loaded",
            "MainPID": "595",