[18.0][ADD] website_blog_scheduled_publication: add new module

[CristianoMafraJunior]

Summary SuperSeed #1159

This PR adds a new module website_blog_scheduled_publication that allows users to schedule blog posts for automatic publication at a specific date and time.

Features

• Scheduled Publication Date: Adds a datetime field to blog posts for scheduling publication
• Quick Publish Button: One-click immediate publication from the form view button box
• Schedule Wizard: User-friendly wizard dialog to set the publication date
• Visual Feedback: Information banner displays the scheduled date on the post form
• Smart Publication Logic: Automatically prevents immediate publication if a future date is set
• Automatic Cron Job: Runs every hour to check and publish scheduled posts
• Notification System: Sends notifications to blog followers when posts are published
• Search Filters: Filter posts by Published/Not Published status and group by Publication Date or Scheduled Publication Date

Technical Details

• Extends blog.post model with new fields (scheduled_publication_date, schedule_type, next_departure) and methods
• Includes a transient model blog.post.schedule.date for the scheduling wizard
• Inherits and enhances form and search views from website_blog
• Handles edge cases: setting past dates, clearing scheduled dates, multiple record writes
• Comprehensive test coverage with 25+ test cases

Dependencies

• website_blog

Test Plan

• Install the module on a clean database
• Create a blog post with a future scheduled date and verify it's not published immediately
• Create a blog post with a past scheduled date and verify it publishes immediately
• Test the Schedule wizard dialog
• Test the Publish Now button
• Run the cron job manually and verify scheduled posts are published
• Verify notifications are sent to blog followers
• Test search filters and grouping options
• Run all unit tests: pytest website_blog_scheduled_publication/tests/

cc @ivs-cetmix @StefanRijnhart