Function parse_select 

pub fn parse_select(
    select: &Value,
    aliases: &CollectAliasMap,
) -> Result<AggregateRequest, QueryDocumentError>

Parse a select object into aggregate request metrics. select value forms: "$record.field", "$alias", "$alias.field", {"$count": "*" | "$alias" | "$alias.field"}, {"$sum": "$record.field"}, {"$avg": ...}, {"$min": ...}, {"$max": ...}.

Errors

Returns QueryDocumentError::Parse for malformed select/collect shapes and QueryDocumentError::Unsupported for unknown select operators.