[EuiTable] Include update message

**Problem Statement**

When table contents update after user actions (filtering, sorting, pagination, search, selection changes), there is no built-in, consistent live announcement from EUI tables.

**Proposed Solution**
Add a top-level EUI table capability to announce updates.
- Provide a generic default announcement (for example, "Table was updated").
- Allow optional customization via prop for more specific messages.

**Use Case**
Teams need accessible feedback for screen reader users whenever table state changes, without re-implementing live announcements in every consumer table. (eg https://github.com/elastic/kibana/issues/242849, https://github.com/elastic/kibana/issues/242898, https://github.com/elastic/kibana/issues/242873)

**Value / Impact**
- Improves baseline accessibility across all EUI table consumers.
- Reduces duplicated app-level accessibility code.
- Provides consistent UX for assistive technology users.

**Do alternatives or workarounds exist?**
Yes. Consumers can add `EuiScreenReaderLive` manually and craft announcements per table flow.
However, this is cumbersome, inconsistent, and sets a pattern where every team must solve the same baseline problem.