Changes at "Improve the email notification for proposal valuators"

Is your feature request related to a problem? Please describe.
Currently, this assigns the \"valuator\" capability to the assigned user, however this does not generate any notification/email to the user.

Describe the solution you'd like
When a valuator is selected to comment on a proposal in the backend system, the valuator receives an email notification including a link to the proposal in the backend system.

Describe alternatives you've considered

Welcome!

Additional context
Technical specifications: openpoke/decidim#18

Implementation (Initial solution): add email notification for proposal valuators openpoke/decidim#23

Does this issue could impact on users private data?

No

Funded by

City of Luzern

*We are aware that there is a redesign policy (https://github.com/decidim/decidim/discussions/9512), but we would like to know if this can be accepted once the redesign is done.