Update bucket E2E test to match the new per-user access model:
- Create bucket with admin (readwrite) and viewer (readonly) users
- Test that readwrite user can upload, list, and download objects
- Test that readonly user can list and download but cannot upload
- Use per-user BucketAccess and credential secret names
Signed-off-by: IvanHunters <xorokhotnikov@gmail.com>