Translate OpenTelemetry Ruby exceptions

# Description

Exceptions captured on Ruby OpenTelemetry traces are not reported in Elastic APM GUI.

See https://github.com/elastic/apm-server/blob/v7.13.4/processor/otel/exceptions.go#L85-L91

```go
func setExceptionStacktrace(s, language string, out *model.Exception) error {
switch language {
case "java":
return setJavaExceptionStacktrace(s, out)
}
return fmt.Errorf("parsing %q stacktraces not implemented", language)
}
```

There were separate issues for .NET, Node.js and Python already. Ruby was missing.
Perhaps there are some other languages missing from [APM Agents](https://www.elastic.co/guide/en/apm/agent/index.html)?

# See Also

* https://github.com/elastic/apm-server/issues/5795
* https://github.com/elastic/apm-server/issues/5800
* https://github.com/elastic/apm-server/issues/5801