Ref. PWA12

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

As a registered participant that's following a participatory process, I receive lots of notifications by email. That overwhelms me, make filters for these kind of messages and defeats the purpose of receiving these kinds of notifications.

Describe the solution you'd like

I want to have a notifications digest. We can start with a summary of notifications in the last 24 hours (daily), but in the future this could also support other kind of timeframes (like weekly, notifications of the last 7 days)

There a couple of things to take into account:

• This should be a setting enabled by default. A participant can change it and go back to old behaviour if she want so. This setting will be called "I want to receive a digest email every day with notifications." and will be available in "My account" -> "Notifications settings". It'll be incompatible with "I want to receive an email every time I receive a notification."
• The digest should contain the notifications related to the activity I follow. As a participant I want to receive a direct notification if someone mentions me or interacts with some content that I have created.
• If there's something to configure server side (crontab or whatever), implementers should have documentation regarding how to set this up.
• It must show the notifications ordered by spaces, for instance if I'm following the

Describe alternatives you've considered

We could also not have a setting for this change, of behaviour, but there could be cases where you actually want to receive 24 hour pings of what's happening in a process, for instance if you're moderating it.

Additional context
See Metadecidim proposal

There are a couple of proposals in Meta:

• https://meta.decidim.org/processes/roadmap/f/122/proposals/15048
• https://meta.decidim.org/processes/roadmap/f/122/proposals/14212

And there was even a PR (#5875) already, but now that I'm reviewing that, there are some doubts regarding the PR: why expire notifications? why there's a limit on how many notifications are sent by email?

Does this issue could impact on users private data?

No, it's just showing other way to send notifications.

Acceptance criteria

• Given that I'm an implementer,
  When I go to https://docs.decidim.org/en/install/#_scheduled_tasks I have instructions on how to set this feature for new apps. (docs/modules/install/pages/index.adoc)
• Given that I'm an implementer,
  When I go to the CHANGELOG I have instructions on how to set this feature for existing apps.
• Given that I'm a participant,
  When I go to "My account" -> "Notifications settings"
  Then I see a new section "How often do you want to receive the notifications emails?" with the options "None", "Real time", "Daily" and "Weekly"
• Given that I'm a participant that had selected "I want to receive an email every time I receive a notification",
  When I go to "My account" -> "Notifications settings"
  Then I have selected the "Real time" option in "How often do you want to receive the notifications emails?"
• Given that I'm a new registered participant,
  When I go to "My account" -> "Notifications settings"
  Then I have selected the "Daily" option by default in "How often do you want to receive the notifications emails?"
• Given that I'm a participant,
  When I have selected the "None" option in "How often do you want to receive the notifications emails?"
  Then I don't receive any notifications emails.
• Given that I'm a participant,
  When I have selected the "Real time" option in "How often do you want to receive the notifications emails?"
  Then I receive emails every time I have a notification.
• Given that I'm a participant,
  When I have selected the "Daily" option in "How often do you want to receive the notifications emails?"
  Then I receive one email with my notifications from yesterday.
• Given that I'm a participant,
  When I have selected the "Weekly" option in "How often do you want to receive the notifications emails?"
  Then I receive one email with my notifications from the last week.