DX-2133: add stringifyBody parameter to context.call and context.invoke

[CahidArda]

By default, all bodies passed to context.call and context.invoke are stringified. This means, if you are calling an endpoint which expects specific strings (imagine "coin=BTC") in the body, the string you passed will be stringified and become '"coin=BTC"' and the API you are calling will return 400.

Since we can't change the default behavior which could break many other workflows, we add a parameter to disable the stringify operation. If stringify is disabled, body needs to be string.

In a future major release we may:

• remove the stringify all together
• require all bodies to be string
• remove this parameter.

in both methods, stringifyBody is true by default. I also added tests to both method to check for different behaviors.

[linear]

DX-2133 workflow-js: add option to pass body as it is in context.call