Migrate "codetag" contrib CKEditor 4 plugin to built-in equivalent in core's CKEditor 5

Problem/Motivation

With CKEditor 4, Drupal core did not provide a code button, even if the HTML tag was accepted by default. T«

Steps to reproduce

1. Install and enable the Codetag module.
2. Add the codetag button to a CKEditor-enabled text format.
   
3. Attempt to upgrade from CKeditor (4) to CKEditor 5.Also, notice the error that the button is not added.
   
4. With proosed fix, switching from CK4 to CK5 does not trigger warning, and the button is present in the same location in the toolbar.
   

Proposed resolution

Replace code with core's CK5 code button.

Remaining tasks

Add the upgrade path.

User interface changes

None.

API changes

New Contrib upgrade class for CK4 -> CK5 plugins