Add filters for dataversions

[jamesliupenn]

Summary

• New dataversions filter field: Adds a dataversions: [String!] input field to CloudEventFilter, allowing callers to filter by multiple dataversion values in a single query using OR logic. The existing singular dataversion field is preserved for backwards compatibility and merged with dataversions into a single In filter.
• Migrate to AdvancedSearchOptions: Switches all resolver calls from the basic SearchOptions/ListIndexes/GetLatestIndex service methods to AdvancedSearchOptions/ListIndexesAdvanced/GetLatestIndexAdvanced. This enables richer filter semantics (e.g. In-based matching) on all filterable fields (id, type, source, producer, subject, dataversion).
• Schema & codegen updates: schema/base.graphqls, models_gen.go, and generated.go are updated to reflect the new dataversions field.
• Test updates: Resolver tests updated to assert against the new In-slice structure rather than single Value fields.