Query params ignored in `invokeFunction`

[mjg123]

This section of code parses the "FunctionId" from the AddInvokeStageRequest:

https://github.com/fnproject/flow/blob/master/model/fnid.go#L26-L42

which includes separating any query params. However these are not correctly propagated to this line:

https://github.com/fnproject/flow/blob/master/actor/executor.go#L96

So it is not possible to invoke a function from a Flow if that function has query params which need to be set.