Address /api/get_total_size timeouts

[kollivier]

Summary

We had reports of /api/get_total_size timing out. We should either optimize the API calls to avoid timeouts, or move the calculation to an async task.

Category

BUG

[jayoshih]

I believe this is part of the import modal, which we don't have the size calculation call for anymore. However, will need to check for other places this might be used

[rtibbles]

This is still being used in the publish modal, so the timeouts could still be a problem.