feature: Support IAM role instead of access / secret keys to use AWS S3 bucket

[withsmilo]

Hi, team.
Some companies force users not to directly own the access / secret keys for AWS S3 bucket. In this case, users can create an AWS IAM role and own the permission for S3 bucket. So it would be good if jnotebook_reader also supports this scenario.

[withsmilo]

@mars-martin-line I'm working on it now.