Use the range selected in Grafana for error budget panels

In &437 we've started with a fixed range calculating a group's error budget over 28d.

In #1033 (closed) we've started recording this data in Sisense.

The fixed range in Grafana could be confusing, because it means that the budget being shown is the 28 days before the end of the range being selected in Grafana:

Proposal

Leave the 28d range in place for the data migration to Sisense, but use the selected range in Grafana.

This would mean that the available budget (currently fixed to ~20 minutes), would be dependant on the size of the range selected. But the panels would still reflect overspend for that range.

This would make it easier for groups to look into their budget for a specific time.