Manually creating projectors causes database consistency check to fail

Describe the bug
Manually creating a projector in the client, without setting is_internal will cause the check_database_all presenter to return a broken verdict. This happens because the client sends null as the value of one field and the backend doesn't stop this.

How To Reproduce

Payload from client (handle_request)
First

[{"action":"projector.create","data":[{"meeting_id":2,"name":"pro jek tor","is_internal":null}]}]

then

[{"presenter":"check_database_all","data":{}}]

Response from backend
For first request

{"status_code": 200, "success": true, "message": "Actions handled successfully", "results": [[{"id": 5, "sequential_number": 3}]]}

For database check

[{"ok": false, "errors": "\tprojector/5: Missing fields is_internal"}]

Expected behavior
The projector.create action should not allow None as a field value for is_internal

Ergo:

1. ensure the backend-action does not allow None for the is_internal field.
2. write a migration to fix any old inconsistencies caused by this

It should also be ensured that projector.update doesn't have the same problem

Reproduce the issue with the shown handle_request payloads, then trace the projector.create and projector.update actions and the check_database_all presenter. Confirm where null is accepted and identify the migration path mentioned in the issue; done means null is rejected for is_internal, existing inconsistencies are repaired, and the database check no longer reports the projector as broken.