SkeletonTable: add option to hide header skeleton rows #968

Description

SkeletonTable always renders skeleton rows for the table header. There is no prop to suppress header skeletons while keeping the body skeleton rows.

Use Case

In ansible/ansible-ui, our PageLoadingTable intentionally omits header skeletons because the real table header (with column titles, sort controls, etc.) is already rendered above the loading state by the toolbar/layout. Showing skeleton header rows creates a visual mismatch — users see the real header and a duplicate skeleton header simultaneously.

Proposed Solution

Add a boolean prop (e.g., showHeaderSkeleton defaulting to true, or numberOfHeaderRows defaulting to 1 with 0 meaning none) to control whether header skeleton rows are rendered.

Current Workaround

We maintain a custom PageLoadingTable component that renders PF6 Skeleton components for body rows only, without header skeletons.

Jira Issue: PF-4546