Document HttpRequest's body handler asynchronous behaviour

[franz1981]

HttpRequest's body handling, with subsequent store of the processed body in a variable, can bite users which expect it to be synchronous with other(s) steps which use its result eg

         scenario:
          - login:
            - pullSharedMap:
                key: policyHolder
                vars: [ email, password, vehicles, insured ]
            - httpRequest:
                endpoint: insurance
                GET: whatever
                headers:
                  accept: application/json
                handler:
                  body:
                    json: .token -> token
         - viewUser:
            - httpRequest:
                endpoint: insurance
                GET: wot
                headers:
                  auth: ${token}
                  accept: application/json

${token} shouldn't assume that token is been set!
Indeed to achieve that ordering should add awaitVar token in viewUser, before httpRequest or in login after httpRequest.