feat: enable downscaling for the number of traces read by AsyncReader

Type of change

• Bug Fix
• Feature

Does this introduce a change in the core logic?

• [No]

Does this introduce a change in the cloud provider implementation, if so which cloud?

• AWS
• Azure
• GCP
• IBM

Updates description?

Provide 'step' parameter to enable downscaling for the number of traces read by AsyncReader; handle 2D index case in ReaderConnector