Use directories.new when getting S3 directory

What does this MR do?

Same as https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/6682:

Calling Fog::Storage::AWS::Directories#get requires the ListAllMyBuckets permission, but we can avoid that extra query and permission by initializing the directory with a specific bucket: https://stackoverflow.com/a/12288581/1992201

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5807

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer