[EuiBasicTable][A11y] Add empty state to table caption

[mgadewoll]

Summary

This PR updates EuiBasicTable by adding additional context information to the table caption about the empty state of the table. This helps to clarify when a table has no columns, as the semantic information still resolves in available columns (header and empty body row) that have no actual data content.

// before
Data table No users found Page 1 of 2.  table  with 2 rows and 7 columns

// after
Data table (empty), No users found, Page 1 of 2.  table  with 2 rows and 7 columns

Why are we making this change?

:accessibility: Accessibility: Increase informational clarity

Screenshots #

Impact to users

🟢 There are no updates required on consumer side.

QA

• [ ] Review the added story with a screen reader and confirm that tables with no items will add an additional "(empty)" text after the tableCaption

General checklist

• Browser QA
  • [ ] Checked in both light and dark modes
  • [ ] Checked in both MacOS and Windows high contrast modes
    • (emulate forced colors if you do not have access to a Windows machine.)
  • [ ] Checked in mobile
  • [x] Checked in Chrome, Safari, Edge, and Firefox
  • [x] Checked for accessibility including keyboard-only and screenreader modes
• Docs site QA
  • [ ] Added documentation
  • [ ] Props have proper autodocs (using @default if default values are missing) and playground toggles
  • [ ] Checked Code Sandbox works for any docs examples
• Code quality checklist
  • [ ] Added or updated jest and cypress tests
  • [ ] Updated visual regression tests
• Release checklist
  • [ ] A changelog entry exists and is marked appropriately
  • [ ] If applicable, added the breaking change issue label (and filled out the breaking change checklist)
  • [ ] If the changes unblock an issue in a different repo, smoke tested carefully (see Testing EUI features in Kibana ahead of time)
• Designer checklist
  • [ ] If applicable, file an issue to update EUI's Figma library with any corresponding UI changes. (This is an internal repo, if you are external to Elastic, ask a maintainer to submit this request)

[elasticmachine]

:green_heart: Build Succeeded

• Buildkite Build
• Commit: 8912c7764652d4ec832b2a4278366d73e8a0322b
• Documentation website
• Storybook

cc @mgadewoll

[elasticmachine]

:green_heart: Build Succeeded

• Buildkite Build
• Commit: 8912c7764652d4ec832b2a4278366d73e8a0322b

cc @mgadewoll