MetricOverviewContainer dataFetch is not rejected when metric data is not found

[openjck]

Because this is a single-page app, even paths which are not found return a 200. For example:

https://data.firefox.com/datasets/desktop/user-activity/Worldwide/nonExistentMetric

When react-refetch tries to fetch a page like this, the dataFetch gets stuck in pending forever, so no error message is ever shown. Switching to a server-side framework like Next.js (#142) would probably solve this. Alternatively, we could host data from a different domain which does return 404s for non-existent paths.

[openjck]

Here's the code in question:

ensemble/src/components/containers/MetricOverviewContainer.js

Lines 43 to 58 in 9b8b66d

	// Due to the way ensemble is currently hosted, this code is not run
	// when metric data is not found.
	//
	// https://github.com/mozilla/ensemble/issues/313
	} else if (dataFetch.rejected) {
	if (dataFetch.reason && dataFetch.reason.message) {
	// eslint-disable-next-line no-console
	console.error(dataFetch.reason.message);
	}
	return (
	<ErrorComponent
	id="metric-overview-fetch-error"
	title="Error fetching metric"
	/>
	);