Allow submitters to edit the submitter list of their own motion

Is your feature request related to a problem? Please describe.
In our case, we want to use OpenSlides for the full organisation of the members assembly, including the submission of motions. Members should be able to create and submit their motions directly in OpenSlides, avoiding unnecessary work caused by submissions via e-mail and manual imports into OpenSlides.

At the moment, changing the submitter list of a motion is tied to the general motion metadata permission.

This creates a permission gap in a common workflow:
Users should be able to add or remove co-submitters for their own motion while the motion is still in an editable state, but they should not be able to edit the metadata of other motions.

Currently, granting the metadata permission is too broad, because it also allows editing metadata such as the status, recommendation, category, and submitter list of motions in general.

Describe the solution you'd like
Submitters should be able to edit the submitter metadata of their own motions. This could be tied either to a workflow setting or to a general motion setting.

Describe alternatives you've considered
One alternative is that authorised users (staff) manually edit the submitter list after being notified by e-mail or other means. However, this creates unnecessary work and administrative overhead.

Start by tracing the motion metadata permission and the UI path for editing a motion's submitter list. Check how editable states and ownership are represented, then define the setting or workflow behavior described in the issue. Done means submitters can add or remove co-submitters on their own editable motions without gaining metadata access to other motions.