Move to yaml-based configuration

This commit updates the configuration to be yaml-based and updates the
configuration to read in a yaml file.

internal/config/validators/files.go

@@ -0,0 +1,27 @@
+package validators
+
+import (
+	"github.com/FAU-CDI/wisski-distillery/pkg/environment"
+	"github.com/FAU-CDI/wisski-distillery/pkg/fsx"
+	"github.com/pkg/errors"
+)
+
+func ValidateFile(env environment.Environment, path *string, dflt string) error {
+	if *path == "" {
+		*path = dflt
+	}
+	if !fsx.IsFile(env, *path) {
+		return errors.Errorf("%q does not exist or is not a file", *path)
+	}
+	return nil
+}
+
+func ValidateDirectory(env environment.Environment, path *string, dflt string) error {
+	if *path == "" {
+		*path = dflt
+	}
+	if !fsx.IsDirectory(env, *path) {
+		return errors.Errorf("%q does not exist or is not a directory", *path)
+	}
+	return nil
+}