opentelemetry: add semconv exception fields (#2310)

When an error value is recorded, it should add the `exception.message`
and `exception.stacktrace` fields from the opentelemetry semantic
conventions to the span/event. Ideally the `exception.type` field would
be provided also, but there is currently not a mechanism to determine
the type name of a trait object.

Co-authored-by: Lily Mara <54288692+lilymara-onesignal@users.noreply.github.com>

Co-authored-by: Lily Mara <54288692+lilymara-onesignal@users.noreply.github.com>