Add verification data export page in stats module

[mllocs]

:tophat: What? Why?

On some occasions, it is necessary to know the sociodemographic data of the participants in a process. Currently, this data can be obtained from the verification form. That is, if you ask for the date of birth, gender, and postal code during the verification, you can then aggregate this data to know the sociodemographic profile of the participants.

:pushpin: Related Issues

• Fixes https://github.com/AjuntamentdeBarcelona/decidim-barcelona/issues/548

:camera: Screenshots (optional)