Override default name convention for Aggregation feature #5994

Is your feature request related to a problem? Please describe.
Currently, aggregation feature name is concatenation of column name and function name. Users should be able to give optional schema name to override it that names it better. It should be inline so it is clear which aggregation feature it is associated with.

Describe the solution you'd like
We should add optional schema field to Aggregation proto.

Describe alternatives you've considered
Adding a schema field in schema section is alternative but may be hard to associate schema field with aggregation feature.