RestController updates should more properly be routed via PATCH

[amcclain]

The update method of RestController binds any data provided to an existing domain object, which makes it a partial update. The corresponding HTTP method should be PATCH, but we instead expect PUT.

See https://www.geeksforgeeks.org/difference-between-put-and-patch-request for one reference.

We should consider a) non-breaking change to start supporting PATCH, then possibly b) breaking change to either remove PUT support or make PUT act as a true PUT, replacing or creating the object in its entirety.