[ML] Improve error handling in Jobs list from failed requests

[peteharverson]

Kibana version: 7.0.0-alpha1-SNAPSHOT

Elasticsearch version: 7.0.0-alpha1-SNAPSHOT

Occasionally the Jobs list will fail to load when a server-side error occurs during the request for data, but rather than the user being presented with an error message, an empty list is displayed saying 'No items found'. The user is given no indication that the request failed, with errors just displayed in the browser console. The list will often display again correctly on a subsequent refresh.

For example, the following screenshot was taken from a deployment with 200 jobs, when the Jobs list failed to load after switching back to the Job Management tab from the Anomaly Explorer. An error {statusCode: 503, error: "Service Unavailable", message: "[search_phase_execution_exception] "} was displayed in the browser console:

If possible, when a server-side request fails, for example due to a failed Elasticsearch query, the error should be propagated back to the client and the user presented with a suitable error message.

cc @stevedodson

[elasticmachine]

Pinging @elastic/ml-ui

[peteharverson]

Closing as client side error handling has been improved by #76743, so details on the error are now propagated back to the user in a toast notification.