✔️ Json Content fetcher

[jon-nfc]

Backend data is in format json, being for both DataSet and for a row from a dataset.

Details

Create a wrapper for the http fetcher that sets up the query for json content.

Reqirements

• same as 3️⃣ HTTP fetcher #220
• Adds json headers for accept
• Adds json headers for content

Tasks

• Create a common json fetcher
• test