[Sharing NG] Add a sharing NG equivalent for the `default_permissions` capability

## Describe the bug
Currently, the capabilities contain `default_permissions` inside the `files_sharing` object to determine the default permissions a link should have upon creating. This permission concept is however deprecated and originates from the old OCS API. Hence we need a new sharing NG equivalent, I guess `default_type`, since this property now determines the permissions of a link.

## Steps to reproduce
1. Check `default_permissions` inside the capabilities response of the server: `https://host.docker.internal:9200/ocs/v1.php/cloud/capabilities`

## Expected behavior
There is some NG equivalent for the `default_permissions` (e.g. `default_type`).

## Actual behavior
We only have `default_permissions`.

cc @rhafer