Selecting an interval that creates too many buckets doesn't show accurate label

[lukasolson]

When you create a visualization with a date histogram, then select an interval that gives you the warning that too many buckets will be created so the interval has been automatically scaled, the label on the visualization should also be updated to show what interval is actually being used, instead of what the user selected.

Take the following example:

I created a date histogram over the last seven days, and selected "Second" as the interval. The warning text tells me that the visualization has been scaled to hour, yet the visualization itself still says "per second".

Related: #6295

[lukasolson]

Duplicate of #8618.