Database optimization with select_related and prefetch_related

[nikochiko]

We make N+1 queries too often where we can get away with using Django optimisations. For example to fetch the workspace for user, or the user / workspace for current saved run / published run.

I haven't kept an exact track of the queries on each request, but I strongly feel like using these optimisations will cut down our queries by more than half.

Where we can do this:

1. during auth (both API and web) - AppUser.objects.prefetch_related('workspace_memberships__workspace__subscription')
2. when rendering workflow pages - SavedRun.objects.select_related('created_by'), PublishedRun.objects.select_related('saved_run', 'created_by', 'workspace__subscription')

Probably more...