Export Dashboard as Template throws HTTP 405

### Build

Detected in OSS nightly build

```
ts=2020-11-19T12:14:46.218754Z lvl=info msg="Welcome to InfluxDB" log_id=0Q_6hJnW000 version=2.0.2 commit=84496e507a build_date=2020-11-19T05:16:09Z
```
### Steps leading to issue

1. Create a dashboard and a cell
1. In the dashboards view click the cog-wheel and export. A popup loads
1. In the popup click the button "Save as Template"

### Expected behavior

A system file management dialog should load and allow the user to save the template as a file in a chosen directory.

### Actual behavior

There is an error message

```
Failed to save dashboard as template: Error: Request failed with status code 405
```

### Screencast