ECS autoscale: honor min/max; tune steps for Falcon

[adiaz04]

Link to Jira ticket

Purpose

Update ECS autoscaling to better match Falcon behavior: respect min/max from callers and reduce aggressive scaling steps.

Approach

• Honor min_number_of_instances and max_number_of_instances kwargs for web autoscaling.
• Reduce scale-out steps (0–5: +1; >5: +2) and increase cooldown to 45s.
• No breaking API changes; defaults preserved.

Testing

• Linted file; no errors.
• Will validate in course-builder staging deployment.

Screenshots/Video

N/A