Proposal to add new resultFormat - to wrap the Druid SQL JSON result array in a JSON object.

### Description

As of `0.16.0`, Druid SQL queries made using JSON over HTTP to the Druid broker would by default return a JSON array of JSON objects (with `"resultFormat": "object"`).

This is an alternative `resultFormat` proposal which is similar to the default `object`, but returns a JSON object wrapping the JSON result array.

### Motivation
Two primary reasons for this proposal:
- This would keep the successful response consistent with the error response, also containing a JSON object as shown [here](https://druid.apache.org/docs/latest/querying/querying.html#query-errors).
- In addition, some serialization formats like JSON<->protobuf today don't support (un)marshaling a top-level JSON array, so a JSON object would be preferred (instead of manually concatenating the JSON array results) - more details can be found [here](https://github.com/golang/protobuf/issues/675#issuecomment-411182202).

The new `resultFormat` will be a JSON object containing a key, for example `"data"`, and then have the resulting JSON array as the value. This is similar to the [“error”](https://druid.apache.org/docs/latest/querying/querying.html#query-errors) response case, where we have `"error"`, `"errorMessage"`, etc., as the keys in the response object.

**Example of current behavior**:
```json
[
{
"page": "Wikipedia:Vandalismusmeldung",
"Edits": 33
},
{
"page": "User:Cyde/List of candidates for speedy deletion/Subpage",
"Edits": 28
},
{
"page": "Jeremy Corbyn",
"Edits": 27
}
]
```
**Proposal format**:
```json
{
"data": [
{
"page": "Wikipedia:Vandalismusmeldung",
"Edits": 33
},
{
"page": "User:Cyde/List of candidates for speedy deletion/Subpage",
"Edits": 28
},
{
"page": "Jeremy Corbyn",
"Edits": 27
}
]
}
```

Start with Druid SQL JSON-over-HTTP responses from the broker and the existing resultFormat "object" behavior; the issue names no files or tests. Review the query-errors response contract and determine the wrapper key, compatibility expectations, implementation scope, and documentation needed before considering the proposal complete.

Written by the indexing model from the issue text.