Add editorSettingsEndpoint to EditorConfiguration

[kean]

What?

• Fix an issue with editor settings not loading for Simple sites. It follows the same approach as used for editorAssetsEndpoint. I intentionally didn't do any refactoring.
• Update EditorService to add query parameters to both the custom and the default endpoints for asset manifest (to keep the behavior consistent with the production version of this API):

URLQueryItem(name: "exclude", value: "core,gutenberg")

Testing Instructions

• (Optional) Use draft integration PR Update GBK WordPress-iOS#25044
• Open the site and the editor
• Verify that the editor settings are loaded, e.g. styles are applied
• Verify that the request URL to fetch settings is constructed correctly, e.g. https://public-api.wordpress.com/wp-block-editor/v1/sites/228225032/settings

[dcalhoun]

Tested well for me. 🚀