Aggregation chart: Add "other" grouping for x-axis labels

Created by: vovakulikov

Follow up for https://github.com/sourcegraph/sourcegraph/issues/39935

On the aggregation chart we could have a lot of labels on the x axis. In order to fit most of them in an appropriate way we have to hide some labels at the end of dataset and group them as Other (or just hide and render number of hidden labels)

See Figma designs for more details

The first version of this could be just adding +n label at the chart container corner.

/cc @joelkw @felixfbecker @vovakulikov @unclejustin