Search: set error boundary for Dashboard

### Impacted plugin

Jetpack, Search

### What

set error boundary for Dashboard

### How

For now we only catch and show API errors, and don't deal with JS errors

Ref: https://reactjs.org/docs/error-boundaries.html

Start with the Jetpack Search Dashboard and review the linked React error-boundaries reference, then compare the existing handling for API errors. Done means JavaScript errors in the Dashboard are caught and shown to users rather than escaping unhandled.

Written by the indexing model from the issue text.