Issue #3575365: Add optional link field to testimonial_item for "Read more" functionality

• Add link field storage and instance configs for testimonial_item
• Update form and view display configs to include the link field
• hook_update_10002: import new field configs for existing installs
• Expose link_url and link_text in template preprocess
• Render link inline inside

  in the twig template

• Add JS truncation (binary search) with inline "… Read more" link
• Register JS in lb_testimonials library with core/drupal, core/once

Before:

After: