Introduced new query parameter for jsonKey

[jfisheratwork]

Often you are only looking for a specific key out of the secret payload. Having each consumer of the agent have to do additional work to parse json and retrieve is error prone.

Look to add parity similar to how it works when retrieving directly from ECS/task definition

Implementation details/concerns:

• As the payload would change should it be a different end point or just an additional query param?
• What type of validation and error codes would be needed for when json key is not present?

I am open to trying to help contribute if issue is excepted