Add a filter to a filter list with the given payload.

Normally you won't have to do this because the filter list is created by calling the "check" function on registered filters when the filter attributes are set, but this does allow more direct manipulation of filter lists when desired.

Note that normally the "check" function can set up a payload for the filter. Using this function, you can either pass in a payload if you know the expected payload format, or you can pass NULL. Some filters may fail with a NULL payload. Good luck!