Add site-level announcements to OJS

[NateWr]

Describe the problem you would like to solve
Multi-journal instances of OJS want to be able to add announcements at the site-level.

Describe the solution you'd like
Add announcements to the admin settings area, so that administrators can add, edit and delete announcements that appear on the site-wide homepage.

The ability to view the latest announcements will be added to the homepage in the default theme. Each site-level announcement will have its own page.

Who is asking for this feature?
This is part of sponsored development work for a PKP|PS client, UNIANDES, who will use this feature in their custom theme.

Implementation

This feature is hidden behind a config flag for 3.4.x and requires a migration to be run manually. Follow these steps to test:

1. Check out the PRs.
2. Add the following to the bottom of your config.inc.php file.

[features]
site_announcements = On

3. Run the following command to run the migration.

php lib/pkp/tools/migration.php \\PKP\\migration\\upgrade\\v3_5_0\\I9253_SiteAnnouncements up

4. Login as an admin.
5. Go to Administration > Hosted Journals and make sure there are two or more journals.
6. Go to Administration > Site Settings > Announcements.
7. Click the checkbox to enable announcements and enter a positive number in the Display on Homepage field.
8. Click the Save button.

Notes:

• When an announcement is sent at the journal level, an email is sent to all users who have subscribed to the journal's announcements. No emails are sent for announcements at the site level because users can not subscribe or unsubscribe to these announcements.
• This PR changes how announcements are ordered in the backend and frontend. Now they are shown with the latest first, by date_posted in descending order.
• This PR fixes a small visual bug in the list of announcements, due to a CSS override, that caused extra padding on the page that lists announcements.
• This only adjusts the default theme. Other themes would need to be modified separately to support this feature.
• This PR also adds support for a featured image with each announcement.

PRs:

stable-3_4_0:
#9255
pkp/ui-library#283
pkp/ojs#4023

main:
#9260
pkp/ui-library#284
pkp/ojs#4028

[NateWr]

The following PRs add support for announcements at the site level to the stable-3_4_0 branch. Once approved, I will port to the other apps and to the main branch. @asmecher can someone review this?

#9255
pkp/ojs#4023
pkp/ui-library#283

This feature is hidden behind a config flag for 3.4.x and requires a migration to be run manually. Follow these steps to test:

1. Check out the PRs.
2. Add the following to the bottom of your config.inc.php file.

[features]
site_announcements = On

3. Run the following command to run the migration.

php lib/pkp/tools/migration.php \\PKP\\migration\\upgrade\\v3_5_0\\I9253_SiteAnnouncements up

4. Login as an admin.
5. Go to Administration > Hosted Journals and make sure there are two or more journals.
6. Go to Administration > Site Settings > Announcements.
7. Click the checkbox to enable announcements and enter a positive number in the Display on Homepage field.
8. Click the Save button.

Notes:

• When an announcement is sent at the journal level, an email is sent to all users who have subscribed to the journal's announcements. No emails are sent for announcements at the site level because users can not subscribe or unsubscribe to these announcements.
• This PR changes how announcements are ordered in the backend and frontend. Now they are shown with the latest first, by date_posted in descending order.
• This PR fixes a small visual bug in the list of announcements, due to a CSS override, that caused extra padding on the page that lists announcements.
• This only adjusts the default theme. Other themes would need to be modified separately to support this feature.

[asmecher]

Reviews added -- thanks, @NateWr!