Use unified S3 connection property names

[morazow]

Situation

Recently, we started initiative to unify S3 connection property names across our projects. This project should also update to those changes.

Acceptance Criteria

• Unified S3 property names are used
• Documentation is updated

[redcatbear]

@Shmuma , please check what the current situation in the code is. The loader can do the new connection style now since quite a while.