Create admin settings fields with GitHub Issues

[leomp12]

1. Create a custom issue template to Add admin settings field:
   https://help.github.com/en/github/building-a-strong-community/configuring-issue-templates-for-your-repository
2. Create a GH Action workflow for issue related event, parse the issue MD body to create JSON and save the value to admin_settings property on ecom.config.json;
3. Then ecom.config.js must import ecom.config.json (as a mock) and merge it;