Provide a way to select which document to generate in web UI

[Sancretor]

Is your feature request related to a problem? Please describe.

As of now, there is now way to select which document (Word, Excel, CSV, Markdown, conf) to generate through the web UI.

Describe the solution you'd like

There should be some checkboxes to enable the user to select which document to generate.
In case none of these checkboxes are checked, there must be a warning message on the screen, explaining that without any document to generate the plugin won't do anything. Moreover, the user must not be able to click on the generate button.
On the plugin API, these parameters must be optional like in the standalone mode.