ROLIE feed is missing feed object

[tschmidtb51]

The ROLIE feeds currently generated by the csaf_provider are missing the surrounding feed element.

Expected output:

{
  "feed": {
    "id": "example-csaf-feed-tlp-white",
    "title": "Example CSAF feed (TLP:WHITE)",
    //...
  }
}

Current output:

{
  "id": "csaf-feed-tlp-white",
  "title": "CSAF feed (TLP:WHITE)",
  // ...
}

[bernhardreiter]

Done (as shown be ROLIE validation not complaining at this point)