feat: use same image for cas api/workers and send worker discord notifs

[smrz2001]

• Added exit code when checking for ECS task status, so that we can detect non-zero exit codes.
• Remove list of anchor workers from in-progress jobs because that was causing Discord messages to get too large.
• Send anchor worker started/completed/failed Discord notifications since we're removing the separate runner image that sent those notifications.
• Use base image when updating worker task def during CAS deployments.
• Don't push CAS runner image to ECR since it's no longer needed.

[linear]

WS2-3214 Replace CAS worker runner script with CD manager reporting

[3benbox]

LGTM