data.json harvest improvements

[kvuppala]

• currently we check the individual dataset json object hash to identify if there are any new updates to the dataset.

• as a first step, we should check the entire json file content hash to make sure there are some updates compared to the previous version, and the next step would be to go into the individual datasets

This additional check improves the harvesting process, and going into the individual dataset hash wont be required if the whole file hash didn't change.