Reports backend investigation

[kookster]

Have a look at how to actually generate reports into a downloadable form.
Here's a few techy questions to sort out off the top of my head, but the issue is for generally trying to figure out how to go about generating reports as a technical problem:

Will we use a new API method on castle to request a report, or is this a different endpoint, like a lambda?

Assuming this is an async process, for the API call, get back a callback url to check to see when it is done being created, or how do we let the user know in the metrics UI when this is ready?

Query the postgres db, or BQ directly?

Could be saved to a file on s3? or is it easier from the google cloud to use their storage?

This is also a user question, but could we make a google drive sheet for the final report instead of a csv file, or as an option?