[spike] Source HubSpot: concurrency

[maxi297]

Investigate how valuable and feasible it is to have HubSpot be concurrent. A couple of points:

• See how many streams syncs using slices
• For stateful streams, ensure that their behavior works with ConcurrentCursor. Else, evaluate the work to make them work
• Check for rate limits
• Check if this could increase the risk of OOM 137
• etc...