Send a notification when a post has been published

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

As a user following a participatory space with a Blog component enabled, when a post is published on the Blog component, I don't receive any notification to encourage me to go and read it.

The user only receives a notification when the Blog component is published, or when posts are interacted with (endorsements, comments, etc.)

Describe the solution you'd like

As an admin, when creating a post without a publication date, or when the publication date is there, I'd like the users following the space to automatically receive a notification by email and on the plaftorm.

Proposed translations:

• Notification title: The %{resource_title} post has been published in <a href="%{resource_path}">%{participatory_space_title}</a>
• Subject: New blog post in %{resource_path}
• Intro: The post "%{resource_title}" has been published in "%{participatory_space_title}" that you are following
• Outro: You have received this notification because you are following this space. You can stop receiving notifications following the previous link.

Describe alternatives you've considered

At first we thought we also needed to implement a publication feature for posts, but then we saw the changes implemented by MainioTech with #9757 and assumilng that's enough to technically implement this notification.

Additional context

Related with this metaproposal and this PR.

Does this issue could impact on users private data?

No

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Le CESE