It would be useful if we could call /charts or /data api endpoints for multiple charts instead of just one by one.
Or maybe this could be some new endpoint similar to /allmetrics but that could take
before parameters too.
Similar to existing endpoints this should return csv or json as defined by the user.
We would need to consider how to handle charts with different
update_every - eg how to make a nice tabular csv of charts with different time frequencies etc.