defaultIndex setting description fix - its really a data view! (elast…

…ic#147730)

## Summary

The defaultIndex setting title and description were poor. I've updated
them to correctly reference data views and be more specific about where
they're used.

Closes elastic#143609

src/plugins/data/server/ui_settings.ts

@@ -166,12 +166,12 @@ export function getUiSettings(
     },
     defaultIndex: {
       name: i18n.translate('data.advancedSettings.defaultIndexTitle', {
-        defaultMessage: 'Default index',
+        defaultMessage: 'Default data view',
       }),
       value: null,
       type: 'string',
       description: i18n.translate('data.advancedSettings.defaultIndexText', {
-        defaultMessage: 'The index to access if no index is set',
+        defaultMessage: 'Used by discover and visualizations when a data view is not set.',
       }),
       schema: schema.nullable(schema.string()),
     },