Add configurable decimal option to single stat widget

What does this MR do and why?

This MR adds a new option for single stat widgets to be used on the Product Analytics dashboards.

If the decimalPlaces value is specified in the visualization YML file, the single stat widget will use that as the value for animate-decimal-places. If not provided, it will default to 0 decimal places (so whole numbers).

Addresses #387532 (closed)

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Dashboard with various decimal places:

One decimal place specified:

Two decimal places specified:

0 decimal places specified if nothing specified:

Five decimal places specified:

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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