feat: Support IGNORE NULLS only for allowed aggregation functions

Currently parser allows to parse queries which IMHO should be failing by unsupported syntax.
Like
`SELECT COUNT(*) IGNORE NULLS FROM (values (1), (null), (2));`

The allowed list for IGNORE NULLS can be found https://github.com/ronsavage/SQL/blob/master/sql-2016.ebnf

Start in the SQL parser entry point that handles IGNORE NULLS and compare its accepted functions with the allowed list in the linked SQL-2016 grammar. Reproduce the COUNT(*) example and add coverage so unsupported combinations fail while allowed aggregation functions continue to parse.

Written by the indexing model from the issue text.