Add "filename" listener to gen2Actor, to archive all generated image files.

The existing mcsExpose Gen2/gen2Actor command explicitly looks for the mcsActor's filename keyword after the mcs expose command has finished.

We are now commanding exposures more indirectly (via the iicActor), but would like to archive PFS image files without creating too much logic in either the iicActor or the gen2Actor to do so.

We will add an MHS keyword callback on all the camera controller filename keywords. All such keywords will cause the given image to be sent Gen2's ocs.archive_framelist() function.