I recently posted a question on the Discourse site about support for array parameters for primitive data types. Unless there are any specific objections to me doing so, I'd like to submit a PR to enable this functionality.

Let me know if this ticket should be in rcl_interfaces instead. Also, if there are any opinions about what the type names should be, I'd like to hear them. I was just thinking we could do, e.g., PARAMETER_DOUBLE_ARRAY.