Add module configuration schema file

Added initial module schema file in merge request MR!4 above at #2.

The config type path used for the routes fields, is inspired from Drupal core system.schema.yml for the 403 and 404 pages path fields, defined on the basic site settings form, see:
https://git.drupalcode.org/project/drupal/-/blob/11.x/core/modules/syste...
without any specific validation constraints or rules.

See the result with config_inspector:

Details:

Any reviews and feedback would be greatly appreciated.
Thanks in advance!