Allow use of "kind" for "runtime" field (overloaded semantic) with warning

Note: in the spec., we made a decision to use the term "runtime" instead of "kind" as used on the CLI as this the word "runtime" is used in conversation and in other Serverless contexts (i.e., "kind" is an OW specific term which is always explained to mean language/lib runtime).

Recently, we have added support for "overloading" field names and it has been requested that we support "kind" to mean "runtime" and to produce a WARNING to the user that "kind" is being mapped to "runtime" and may be deprecated in the future.