Issue Summary

This is reproducible on Data Center: (yes) / (no)

Currently, there is no V2 REST API endpoint to add attachments.  It would be nice to have this endpoint added for parity even if the V1 endpoint to add attachments is not marked as deprecated (since they use different granular scopes).

Steps to Reproduce

1. Check https://developer.atlassian.com/cloud/confluence/rest/v2/api-group-attachment/#api-group-attachment

Expected Results

Together with the one to GET attachments, there should also be a POST endpoint to add them.

Actual Results

The "add attachment" endpoint is missing

Workaround

Use the V1 endpoint -> /wiki/rest/api/content/{id}/child/attachment which has not been marked as deprecated.