Add sentinel state API endpoint

Add endpoint for sentinel components state.

It would return data based on following json schema:

{
   "definitions": { 
      "sentinel_service_state": {"enum": ["disabled", "failed", "running", "sending", "unknown", "uninstalled"]}
   },
   [...]
   {
            "description": "Reply to get sentinel components state",
            "properties": {
                "module": {"enum": ["sentinel"]},
                "kind": {"enum": ["reply"]},
                "action": {"enum": ["get_state"]},
                "data": {
                    "type": "object",
                    "properties": {
                        "fwlogs": {"$ref": "#/definitions/sentinel_service_state"},
                        "minipot": {"$ref": "#/definitions/sentinel_service_state"},
                        "survey": {"$ref": "#/definitions/sentinel_service_state"},
                        "proxy": {"$ref": "#/definitions/sentinel_service_state"}
                    },
                    "additionalProperties": false,
                    "required": ["fwlogs", "minipot", "survey", "proxy"]
                }
            },
            "additionalProperties": false
        }
}

https://gitlab.nic.cz/turris/foris-controller/foris-controller-sentinel-module/-/blob/master/foris_controller_modules/sentinel/schema/sentinel.json#L328-348