Support for GROUP BY/HAVING

### Component

GraphQL Engine

### Is your proposal related to a problem?

Currently running into a situation with row group using ag-grid where a solution is needed for getting the counts of an unknown set of columns.

```
SELECT state, category, count(*)

WHERE state = 'COMPLETED'

GROUP BY state, category;
```

The view method won't work because the list of columns in the group by is dynamic based on what columns the user decides to group.

### Describe the solution you'd like

Add GROUP BY/HAVING

The issue names no files, tests, or entry points. Start by reviewing the GraphQL Engine's existing view method and how it handles dynamic column selections; define how GROUP BY and HAVING should support ag-grid's unknown grouping columns, with completion demonstrated by coverage for the requested query behavior.

Written by the indexing model from the issue text.