Patterns editable rich text fields: ensure Cmd/Ctrl-K shortcut works to insert links


Based on the feedback from:

- https://github.com/WordPress/gutenberg/pull/71730#issuecomment-3527782646

The Cmd/Ctrl-K shortcut should be enabled in pattern content items' rich text fields so that users can insert links as they can in the editor.

https://github.com/user-attachments/assets/54c3d5f6-2a71-47d6-b275-9fd5d8034f1f
