Push down aggregation through filter into table scan

[findepi]

Consider query

SELECT count(*)
FROM sales
WHERE account = 'Important customer'
GROUP BY account

which will be planned as:

- Aggregation: count(*)
  - Filter: account = 'Important customer'
    - TableScan

The ideal connector behavior will be to

• accept filter in ConnectorMetadata#applyFilter
• Filter is removed from the plan
• accept aggregation in ConnectorMetadata#applyAggregation

However, for some connectors this will be hard to achieve.
For example, for a database doing case insensitive comparisons, we may need to
retain Filter on the Presto side.
In such a case, we could attempt ConnectorMetadata#applyAggregation "through Filter"
leveraging the fact that the filter is on the aggregation keys.

(Thanks @sopel39 for spotting this!)

Relates to: #4137

[findepi]

For example, for a database doing case insensitive comparisons, we may need to
retain Filter on the Presto side.
In such a case, we could attempt ConnectorMetadata#applyAggregation "through Filter"
leveraging the fact that the filter is on the aggregation keys.

In such a case, pushing down aggregation would not be correct.