Super Cache: notify Boost that migration is in progress

[donnchawp]

Fire an action "jb_cache_moved_to_boost" that lets Jetpack Boost know of a migration from WPSC to Boost.

Fixes #37742

Proposed changes:

• Create a function "wpsc_notify_migration_to_boost" that creates a transient option called "jb_cache_moved_to_boost" with a $source as the value.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

pc9hqz-2QH-p2

Does this pull request change what data or activity we track or use?

Testing instructions:

No user visible changes as it sets a transient option.
Add this line to wpsc_ajax_activate_boost(), jsut above wp_send_json_success();

	wpsc_notify_migration_to_boost( 'banner' );

Add the following mu-plugin to hook on the action and log the source:

function test_jb_cache_moved_transient() {
    if ( get_transient( 'jb_cache_moved_to_boost' ) ) {
        error_log( 'transient: ' . get_transient( 'jb_cache_moved_to_boost' ) );
    }
}
add_action( 'admin_init', 'test_jb_cache_moved_transient' );

Make sure that Boost is entirely deleted from the plugins directory and reload the WPSC settings page. If you have previously dismissed the Boost banner you will need to delete the wpsc_dismissed_boost_banner user option for your user.
Click the "Install Jetpack Boost" or "Activate Jetpack Boost" button and watch the error_log.

[github-actions]

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Super Cache plugin:

• Next scheduled release: July 2, 2024.
• Scheduled code freeze: June 24, 2024.

If you have any questions about the release process, please ask in the #jetpack-releases channel on Slack.

[dilirity]

Nice.

This helps us move the migration forward.