Add recipe for cosmic-files

recipes/gui/cosmic-files/manifest

+name=COSMIC File Manager
+binary=/bin/cosmic-files
+icon=/ui/icons/apps/system-file-manager.png
+author=Jeremy Soller
+description=COSMIC File Manager

recipes/gui/cosmic-files/recipe.toml

+[source]
+git = "https://github.com/pop-os/cosmic-files.git"
+branch = "master_jammy"
+
+[build]
+template = "custom"
+script = """
+cookbook_cargo --no-default-features
+mkdir -pv "${COOKBOOK_STAGE}/ui/apps"
+cp -v "${COOKBOOK_RECIPE}/manifest" "${COOKBOOK_STAGE}/ui/apps/cosmic-files"
+"""