Specify location of the temporary bucket

Would be nice to be able to specify the region/s in which the temporary upload bucket is in.

Review how the plugin creates and configures its temporary upload bucket, then determine where a region or set of regions could be exposed. No file, test, or entry point is named in the issue, so first locate that bucket-handling path and its existing configuration. Done means users can select the temporary bucket location and the behavior is covered by appropriate tests.

Written by the indexing model from the issue text.