Infer service name and set it at startup

## Is your feature request related to a problem?
If service name is not explicitly set (using the [two options](https://opentelemetry.io/docs/languages/sdk-configuration/general/#otel_service_name)) then there is a generic default `unknown_service`. This is not useful for auto-instrumentation

## Describe the solution you'd like
The service name should be inferred as best as possible, if some property is set to true (eg OTEL_ELASTIC_AUTO_SERVICE_NAME=true).

## Describe alternatives you've considered
Suggestions welcome

## Additional context
While in most cases you can ask the user to set the service name explicitly - which is best practice - in the case of [zero-code configuration](https://opentelemetry.io/docs/zero-code/java/) this would add additional per deployment configuration which is not the optimal experience