Add visibilityLevel to Ci::Catalog::Resource type in GQL

What does this MR do and why?

Add visibilityLevel to Ci::Catalog::Resource in order for FE to add it to the list and details page. Designs here: #480522

MR acceptance checklist

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For one resource:

{
  ciCatalogResource(fullPath: "gitlab-org/public-catalog-resource") {
    visibilityLevel
  }
}

{
  "data": {
    "ciCatalogResource": {
      "visibilityLevel": "public"
    }
  }
}

For all resources:

{
  ciCatalogResources {
    visibilityLevel
    name
  }
}

{
  "data": {
    "ciCatalogResources": {
      "nodes": [
        {
          "visibilityLevel": "public",
          "name": "public-catalog-resource"
        },
        {
          "visibilityLevel": "private",
          "name": "private-catalog-resource"
        }
      ]
    }
  }
}

NOTE: We do not care about internal projects at the moment.