feat: Create parent directories if --split-exp is used.

Problem: When --split-exp is used and produces filenames with slashes in
them, the target directories must already exist otherwise yq fails.

Fix/feature: Create the necessary directories with os.MkdirAll().
The permissions 0750 were chosen to satisfy the vulnerability checker.

cmd/root.go

@@ -197,7 +197,7 @@ yq -P -oy sample.json
 	}
 	rootCmd.PersistentFlags().BoolVarP(&yqlib.ConfiguredYamlPreferences.LeadingContentPreProcessing, "header-preprocess", "", true, "Slurp any header comments and separators before processing expression.")
 
-	rootCmd.PersistentFlags().StringVarP(&splitFileExp, "split-exp", "s", "", "print each result (or doc) into a file named (exp). [exp] argument must return a string. You can use $index in the expression as the result counter.")
+	rootCmd.PersistentFlags().StringVarP(&splitFileExp, "split-exp", "s", "", "print each result (or doc) into a file named (exp). [exp] argument must return a string. You can use $index in the expression as the result counter. The necessary directories will be created.")
 	if err = rootCmd.RegisterFlagCompletionFunc("split-exp", cobra.NoFileCompletions); err != nil {
 		panic(err)
 	}