Instance stats: fetch data points within a date range

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Summary

As a follow up to #268000 (closed) we should update the instance usage trends charts FE requests to make use of date ranges for determining the amount of data that needs to be fetched.

Implementation guide

• Add support for the recordedAfter and recordedBefore variables to https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/analytics/usage_trends/graphql/queries/usage_trends_count.query.graphql
• Remove the totalDaysToShow and use the selected date range instead

Improvements

Currently we need to calculate the number data points to fetch on the FE as well as tracking how many we have fetched, this change will allow us to simply query for all data within the specified date range.