Unable to add new content blocks, optional compounds and multi-value properties from the Visual Editor

This functionality is working as expected on the latest v15 so it is a regression bug introduced in v16.
This bug affects any value that can be added from the Visual Editor eg. content blocks, optional compound fields, multi-value fields

Reproduction steps:

1. Run the attached archetype project
2. Go to the news section
3. Create a new news document from the + button (Edit content) in the Experience Manager
4. Fill in the name and click Next
5. IMPORTANT: Before clicking Save as draft or Create try to add one of the two compounds to the CTA field

Expected result:

The selected compound gets added to the CTA field

Actual outcome:

"Failed to add a field value" is displayed and the following warnings are printed in the logs

WARN  http-nio-8080-exec-6 [RepositoryJaxrsService$WebApplicationExceptionLogger.toResponse:300] jakarta.ws.rs.ClientErrorException: HTTP 405 Method Not Allowed

WARN  http-nio-8080-exec-4 [RepositoryJaxrsService$WebApplicationExceptionLogger.toResponse:300] jakarta.ws.rs.ClientErrorException: HTTP 404 Not Found

WARN  http-nio-8080-exec-8 [RepositoryJaxrsService$WebApplicationExceptionLogger.toResponse:300] jakarta.ws.rs.ClientErrorException: HTTP 404 Not Found

Lef's Investigation:

v15 network call is POST to http://localhost:8080/cms/ws/content/documents/a801d686-091f-4135-a61c-4783a27d10b4/editable/v15:cta/v15:External

which triggers
@POST
@Path("documents/{documentId}/editable/{fieldPath:.*}/{type}")
 from org.onehippo.cms.channelmanager.content.ContentResource 

v16 network call is POST to http://localhost:8080/cms/ws/content/documents/editable/v16:cta/v16:External (missing the {documentId} section of the expected Path param) as a result it doesn't trigger the above mentioned POST/Path

Seems like the logic in the frontend code of the channel manager/visual editor has changed.