Allow sidecar files alongside monthly SWY inputs

[phargogh]

The SWY model has some reasonably strict restrictions on what files are allowed in the monthly SWY input folders. If we want to encourage and support the use of metadata files (MCF or ISO or whatever), those metadata files should remain alongside the monthly files. So the model should know to exclude the non-raster metadata files that are sitting alongside the raster itself.

This came up in the NatCap labs conversation 2024-02-05.