Send email to the author when a content is hidden

[microstudi]

Original requirement:

As a user, I would like to receive a notification if my proposal is hidden.

Context

Currently, when a content is moderated, the admin can decide to hide the proposal or, if the number of reports exceeds the configuration Decidim.max_reports_before_hiding.
This is done by the Decidim::Admin::HideResource command. Which results on hiding the proposals and creating a notification on the user who created the proposal, but it does not send and email.

User notification:

Admin hide/moderation:

Tasks

• Add a mailer job sending the authors of a moderated resource a notice that their proposal has been hidden.
• Add tests

Possible email content:

An administrator removed your proposal because it has been reported as spam:

%{resource_title}

If you feel that has been a mistake please contact the administrators of %{organization} (with link to the decidim url)

• branch from release/0.26-stable, PR to this repository, same branch