Azure Guidelines: Determine need for and guidance on 100-Continue

[markweitzel]

We have encountered few situations where a "look before you leap" request pattern has been used. This can be useful for requests that are expected to return a large payload. However, its application has been so rare that, at this point, there has not been a need to provide prescriptive guidance. We are going to determine if this is a more pervasive pattern that previously thought, and if so, craft the appropriate guidance.