Configure deployment to target Onramp augmented diffs

We'll need to update streaming-augdiff-producer script defined [here](https://github.com/azavea/osmesa/blob/develop/deployment/streaming/scripts/define-streaming-augdiff-producer.sh#L27) to include a `-s onramp` in the task `command` when the `ONRAMP_URL` is not an empty string.

Start with deployment/streaming/scripts/define-streaming-augdiff-producer.sh at the task command around line 27, and inspect how ONRAMP_URL is handled. Done means the command includes -s onramp when ONRAMP_URL is non-empty and remains unchanged when it is empty.

Written by the indexing model from the issue text.