Detect site-url changes

[aristath]

Detects site-url changes.
If the site URL has changed, makes a request to a new endpoint on our server.
That endpoint then updates the entry in our database for the newsletters etc.
Of course that only happens if the site is already registered to get newsletters.

Depends on https://github.com/ProgressPlanner/progress-planner-server/pull/47

[github-actions]

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[Copilot]

Pull Request Overview

This PR implements site URL change detection functionality to notify the remote server when a WordPress site's URL has changed. This enables automatic updates to the database for newsletter registrations and other site-dependent data.

Key changes:

• Added site URL change detection that runs on WordPress shutdown hook
• Refactored remote URL handling to use a single parameterized method
• Updated references to use the new consolidated URL method

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
classes/utils/class-onboard.php	Added site URL change detection method and consolidated remote URL handling
classes/admin/class-page.php	Updated to use the new parameterized remote URL method

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