…anager UI (elastic#271377)

Two `EuiInMemoryTable` instances in the drilldown manager UI were
missing the required `tableCaption` prop, violating
`@elastic/eui/require-table-caption`.

### Changes

- **`drilldown_template_table`** — Added `tableCaption` with i18n
string: *"Drilldown templates"*
- **`drilldown_table`** — Added `tableCaption` with i18n string:
*"Drilldowns"*

```tsx
<EuiInMemoryTable
  tableCaption={txtTableCaption}
  items={drilldowns}
  // ...
/>
```

Captions describe the dataset per EUI accessibility guidelines and use
`i18n.translate` for localization.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Alexey Antonov <alexwizp@gmail.com>
(cherry picked from commit fa6e1f1)