[enchrichment] support span eventName `error`

Should we support `error` event name in [addition to `exception`?](https://github.com/elastic/opentelemetry-lib/blob/main/enrichments/internal/elastic/span.go#L672)

[Semconv states](https://opentelemetry.io/docs/specs/semconv/exceptions/exceptions-spans/) the eventName must be `exception` however there seems to be a lot of usage of events with `error` `eventName` not being picked up. I experience this with the otel-demo, described in this issue https://github.com/open-telemetry/opentelemetry-demo/issues/2905.

A search also reveals some usages: https://github.com/search?q=span.AddEvent%28%22Error%22%2C+trace.WithAttributes%28+language%3AGo&type=code