API /api/v1/workflow-templates seems to be undocumented

### Pre-requisites

- [x] I have double-checked my configuration
- [x] I have tested with the `:latest` image tag (i.e. `quay.io/argoproj/workflow-controller:latest`) and can confirm the issue still exists on `:latest`. If not, I have explained why, **in detail**, in my description below.
- [x] I have searched existing issues and could not find a match for this bug
- [x] I'd like to contribute the fix myself (see [contributing guide](https://github.com/argoproj/argo-workflows/blob/main/docs/CONTRIBUTING.md))

### What happened? What did you expect to happen?

The public documentation lists only `/api/v1/workflow-templates/{namespace}`, and I don't see `/api/v1/workflow-templates` documented here.

https://argo-workflows.readthedocs.io/en/latest/swagger/

Is this just a mistake? Happy to update docs/swagger to clarify that `namespace` is not a required parameter as the docs says.

### Version(s)

ALL

### Paste a minimal workflow that reproduces the issue. We must be able to run the workflow; don't enter a workflow that uses private images.

```YAML
NA
```

### Logs from the workflow controller

```text
NA
```

### Logs from in your workflow's wait container

```text
NA
```

Start by reviewing the API documentation under docs/swagger and compare the documented /api/v1/workflow-templates/{namespace} endpoint with the public API behavior described in the issue. Done means the documentation clearly explains whether namespace is optional and includes the /api/v1/workflow-templates endpoint as needed.

Written by the indexing model from the issue text.