Revisit and Improve documentation on Refresh and Update endpoints

[james-rae]

In the Service Contract , revist the documentation around refresh and update (and compare against the code).

In particular:

• update doc claims it has no request body, but this does not appear to be the case. add param and details around the param if required.
• if refresh is just calling update against a batch of keys, indicate that

[barryytm]

After taken a look at the codes. Here are a couple things that I've concluded and please correct me if I am wrong.

• update does has a request body and even Request Params indicated that, it appeared to be just a small mistake in the docs. service_type is the only mandatory field/param in update that was being used.
• refresh is not calling update but rather recreating the nodes against the registered keys.

[barryytm]

Just to clarify. update also uses any other fields that require updating on a pre-registered entry as mentioned in the service contract but they are not required.