Add "description" textarea for API Endpoints

Problem/Motivation

Thank you for continuing this wonderful module in Drupal 8+! This is great!

Just one possible future improvement: For more complex (or many) Service Endpoints defined, it would be super helpful to not only have a title and machine name, but also to be able to add a description for the Endpoint.

That description should be shown in the table of all Service Endpoints and be editable in a textarea.

Thank you very much in advance!

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes