Add sort list generic type argument for Panache REST Data

[MikeEdgar]

Minor improvement to support OpenAPI documentation for the list endpoint
Before:

{
  "name": "sort",
  "in": "query",
  "schema": {
    "type": "array"
  }
}

After, items is present

{
  "name" : "sort",
  "in" : "query",
  "schema" : {
    "type" : "array",
    "items" : {
      "type" : "string"
    }
  }
}

[quarkus-bot]

✔️ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

[gsmet]

Thanks!