add option to track on which page the survey was taken

[sgratzl]

there is no option to add a hidden field in a google form. However, we can add a field that is visible to the user but filled out automatically, e.g.: currently viewed page: ...

[sgratzl]

the website is already prepared for prefilling a field, e.g. when adding a form field and update the url in the config.toml, one could add:

where the field is automatically filled when the survey is opened.