Disable ETUI for piped input (#571)

* fixed piped input

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* allow pipedinput helper to raise an error

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

* factor out verbosity check to function

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

internal/input.go

@@ -0,0 +1,16 @@
+package internal
+
+import (
+	"fmt"
+	"os"
+)
+
+// IsPipedInput returns true if there is no input device, which means the user **may** be providing input via a pipe.
+func IsPipedInput() (bool, error) {
+	fi, err := os.Stdin.Stat()
+	if err != nil {
+		return false, fmt.Errorf("unable to determine if there is piped input: %w", err)
+	}
+
+	return fi.Mode()&os.ModeCharDevice == 0, nil
+}