Fix GraphQL aggregation features disabled when runtime.graphql config section is absent

[Copilot]

Why make this change?

GraphQL aggregation features (groupBy, sum, avg, min, max, count) were silently disabled for users whose config lacked an explicit runtime.graphql section, even though EnableAggregation defaults to true.

What is this change?

Bug fix: RuntimeConfig.EnableAggregation logic inversion

The property used && logic, returning false when Runtime or Runtime.GraphQL was null. This is inconsistent with every analogous property (e.g. IsGraphQLEnabled) which use || logic to treat absence as "use default (enabled)":

// Before (broken): returns false when runtime.graphql section is absent
public bool EnableAggregation =>
    Runtime is not null &&
    Runtime.GraphQL is not null &&
    Runtime.GraphQL.EnableAggregation;

// After (fixed): returns true when section is absent, consistent with IsGraphQLEnabled
public bool EnableAggregation =>
    Runtime is null ||
    Runtime.GraphQL is null ||
    Runtime.GraphQL.EnableAggregation;

Additional fixes:

• GraphQLSchemaCreator.OnConfigChanged now updates _isAggregationEnabled on hot-reload (was omitted, causing stale state)
• schemas/dab.draft.schema.json: added enable-aggregation to runtime.graphql properties — it was missing despite additionalProperties: false, meaning any config explicitly setting the flag would fail schema validation

How was this tested?

• Integration Tests
• Unit Tests
  • 4 new RuntimeConfigLoaderTests: EnableAggregation defaults to true when runtime or runtime.graphql sections are absent; correctly honours explicit true/false
  • 3 new QueryBuilderTests: groupBy field added to connection type for MSSQL (supported), absent for PostgreSQL (not in AggregationEnabledDatabaseTypes), absent when disabled

Sample Request(s)

With a config that has no explicit runtime.graphql section, the following now works as expected for MSSQL/DWSQL entities:

{
  books {
    groupBy(fields: [price]) {
      fields { price }
      aggregations {
        count
        sum(field: price)
        avg(field: price)
        max(field: price)
        min(field: price)
      }
    }
  }
}