Create configuration form for menu_title_length value

Hi

I Reviewed the MR!3 it added configuration for url: "admin/config/system/menu-title-length/settings", For reference adding Screenshot of it.

keshav.k → made their first commit to this issue’s fork.

Added the schema.yml and settings.yml files fro configuration to set default value to configuration.
Please review.
Thank you.

I have reviewed & merged above code in latest version.