feat(metadata-view): bulk custom actions

[jpan-box]

Assumptions:

• Ellipses icon should show when one or more rows have been selected
  • Therefore, the ellipses "bulk action" icon only shows if Select All is also enabled in the tableProps
• No icons or subactions
• Selecting an action triggers an onClick handler (provided by the consumer) which receives all selected Item Ids.

Summary by CodeRabbit

• New Features

  • Bulk actions dropdown added to the Content Explorer sub-header and shown when items are selected; supports configurable actions.

• Accessibility

  • ARIA label added to the Bulk actions control for improved screen-reader support.

• Style

  • Added spacing to the Bulk actions trigger for improved layout.

• Tests

  • Storybook visuals and unit tests updated to cover bulk-action visibility, menu interactions, and callback invocation.