Set default make_http_request body to nil

What does this MR do and why?

Followup from !1243 (comment 1675714217)

While the HTTP spec does allow a GET request contain a body, the semantics of such requests are undefined. Therefore it is often considered best practice to not include a payload on a GET request.

This has caused issues in the past such as this failure where dockerhub began to return errors with a payload of "{}" but worked with nil. gitlab#433330 (closed)

To avoid any other such unexpected failures on GET requests, let's instead assume that by default the GET request will have a nil payload and allow a caller to pass the payload when required.

How to set up and validate locally

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