render - formats should include model

### Feature description

Currently Grails controllers render json with no model. This is extremely limiting and contrary to how other views work. For instance, def index() provides `"${entityName.uncapitalize()Count}"` to index.gsp, but index.json just returns a json list with no count.

Meta data is crucial for being able to properly paginate through large amount of results or even providing context.
Proper pagination should use cursors instead of offsets and using the default rendering strategy provides no mechanism for providing this meta data.

The default should be changed to a structure that provides data and meta data.
A possibility is:
```json
{
"data": [ /* the list */ ],
"meta": { /* the model */ },
}
```
For example:
```json
{
"data": [ { "name": "Bob", "id": 1 }, ... ],
"meta": { "count": 100, "cursor": "aSdFa123" }
}
```

https://jsonapi.org/format/#fetching-pagination

Start by tracing how Grails controllers render JSON for index actions and how index.json differs from index.gsp. Review the JSON:API pagination guidance linked in the issue, then define the data and metadata structure and verify that counts and cursor information are exposed without breaking existing rendering behavior.

Written by the indexing model from the issue text.