Canvis a "Expand meeting notifications"

Is your feature request related to a problem? Please describe.
Currently, whenever a meeting is updated, Decidim sends out notifications (and emails) to the users registered to or following the meeting. However, these notifications always have the same structure, i.e.:

Hi XX

The \"%{resource_title}\" meeting was updated. You can read the new version from its page:

Link

Original text:

The description text from the meeting goes here.

You have received this notification because you are following the \"%{resource_title}\" meeting. You can unfollow it from the previous link.

This notification is sent regardless of what is changed (i.e. just an address, the date and time or something else). This is highly confusing, because the text that is sent may have nothing to do with the updated information, but the participant perceives that it does.

Describe the solution you'd like
I would like the notification to include what actually changed in the meeting. This should happen for updated time, address, registration status, services, description text, title etc.

Example for and updated location:

Hi XX

The meeting \"%{resource_title}\" was updated.

Old address:

Old address (strikethrough)

New address:

New address

You can visit the meeting through this link:

Link

You have received this notification because you are following the meeting \"%{resource_title}\". You can unfollow it from the previous link.

Additional context
We may have to find a way how to bundle this information if multiple things change (i.e. if a process admin changes multiple things and save every time in between) so as to not spam the user.

Does this issue could impact on users private data?
No

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