Settings service user can list other peoples assignments

## Context
oCIS version: v2.0.0-rc.1

## Issue
A normal user can list other users assignments. In this case Einstein can list the admins assignments:
```
curl -k -s -u einstein:relativity -X POST 'https://localhost:9200/api/v0/settings/assignments-list' -d '{"account_uuid":"be65710a-bced-465e-9e1a-72ff269de8ee"}' | jq .

{
"assignments": [
{
"id": "30879be8-bb6f-4248-9188-df3ef6a772f7",
"accountUuid": "be65710a-bced-465e-9e1a-72ff269de8ee",
"roleId": "71881883-1768-46bd-a24d-a356a2afdf7f"
},
{
"id": "f03dacd1-314b-4561-8654-6e729555324a",
"accountUuid": "be65710a-bced-465e-9e1a-72ff269de8ee",
"roleId": "71881883-1768-46bd-a24d-a356a2afdf7f"
},
{
"id": "98dad15a-46aa-4302-9c41-6e3d6d4f0813",
"accountUuid": "be65710a-bced-465e-9e1a-72ff269de8ee",
"roleId": "71881883-1768-46bd-a24d-a356a2afdf7f"
},
{
"id": "94a64f94-1219-46fb-b950-fd1487f453ee",
"accountUuid": "be65710a-bced-465e-9e1a-72ff269de8ee",
"roleId": "71881883-1768-46bd-a24d-a356a2afdf7f"
}
]
}
```

## Expected

I don't know right now if there are valid cases where this would make sense but intuitively I'd say that this should be prohibited.