Implement event details

[sameerank]

#207 adds the eventing functionality in accordance with the 5.x requirements.

However the implementation of event details is incomplete: https://openfeature.dev/specification/types#event-details

It only exposes the one required field in the spec: provider_name

ruby-sdk/lib/open_feature/sdk/configuration.rb

Line 241 in 9107058

event_details = {provider_name: provider_name}

We should include the others for completeness: flags_changed, message, error_code, metadata

The Python SDK may be a helpful example to cross reference: https://github.com/open-feature/python-sdk/blob/837fef943e9585640975258ccf0d095faacf740b/openfeature/event.py#L31-L38