Allow returning arrays when using Input 'JSON path value from HTTP API'

## What?

Currently the Input 'JSON path value from HTTP API' is only designed and is capable of returning a single value from the specified json path.

See https://github.com/Graylog2/graylog2-server/issues/13344

It would be useful to have the ability to return arrays (objects) from the JSON path result in the format of valid json. While json path does return the specified values, the json is invalid and cannot be used with any Graylog Pipeline json functions. Most every API that returns JSON will return objects.

## Why?

Currently the JSON HTTP API Input is limited in use and functionality because it either can only return a single value, or return invalid json when attempting to return multi values.