Allow normalizing event bar charts by session count

### Problem Statement

When reviewing crashes (or really any error), it can be useful to understand if there was a certain point in time where there was suddenly a huge influx of crashes. The bar chart on issue pages could be a useful tool for this purpose, but due to a lack of any way to normalize the counts by number of sessions this becomes very difficult.

For example, if I see a spike on an issue such that there are 50x more events today than yesterday, that _could_ be meaningful to help track down the cause - unless it was because we had 50x more sessions that day, in which case the spike is likely meaningless.

### Solution Brainstorm

My thought would be that the event bar chart on the issue page should have some "view" options to show the raw count or to normalize by session count in the same time period for each bar. It would be useful to have the same options for dashboards as well.

### Product Area

Issues

The issue names no files, tests, or entry points. Start by locating the event bar chart on issue pages and the corresponding dashboard chart, then determine how their view options and session counts are provided; done means users can switch between raw counts and session-normalized values for each time period.

Written by the indexing model from the issue text.