expand product_request() and (maybe) deprecate ExecutionRequest

[cosmicexplorer]

See this comment by @stuhood in #5943. product_request() or product_requests() are (in my opinion) easier to use than the ExecutionRequest API, and don't introduce a (seemingly) unnecessary step of creating a request to be executed. There are few enough users of ExecutionRequest that we can consider deprecating it, if we can add a "list of tuples" type method (described in the linked comment) for the product_request() family of methods.

[Eric-Arellano]

Closing as this has been superseded by the V2 engine / Rules API.