deprecation msgs for KUBECTX_CURRENT_{BG,FG}COLOR

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

internal/cmdutil/deprecated.go

@@ -0,0 +1,22 @@
+package cmdutil
+
+import (
+	"io"
+	"strings"
+
+	"github.com/ahmetb/kubectx/internal/printer"
+)
+
+func PrintDeprecatedEnvWarnings(out io.Writer, vars []string) {
+	for _, vv := range vars {
+		parts := strings.SplitN(vv, "=", 2)
+		if len(parts) != 2 {
+			continue
+		}
+		key := parts[0]
+
+		if key == `KUBECTX_CURRENT_FGCOLOR` || key == `KUBECTX_CURRENT_BGCOLOR` {
+				printer.Warning(out,"%s environment variable is now deprecated", key)
+		}
+	}
+}