Configure S3 buckets to not be indexable by search engine crawlers

Currently the publicly viewable files we store in S3 for users is being indexed by at least google, and continues to be indexed if the files are removed from S3. We would like to prevent this indexing somehow, as we only want the files accessed via the DemocracyLab platform.

The issue identifies publicly viewable user files in S3 as the scope but names no repository files or tests. Start by locating the S3 bucket configuration and checking how files are exposed; done means crawler indexing is prevented while intended DemocracyLab access still works, including removed-file search results.

Written by the indexing model from the issue text.