I would like to set a default value for date range filter field in charts, e.g by default have it set to the past 30 days
This is the same way you can set a default in the filter fields for an assigned record or even status, for example.
As the data in a chart grows, it can take a while to load up - having a default that we can set it to ( e.g., the last 30 days )makes it more relevant for the user and also hopefully improves the load-up speed.