Dont forcefully set service_name option on any exporter

[cedricziel]

Some exporters do not define this option (OTLP f.e.) and setting this option
breaks them.

[tidal]

@cedricziel
Thanks for your contribution and sorry again for the late response.
As I mentioned on slack, we are busy setting up the infrastructure to have better 2e2 test at the moment.

There is one integration test failing due to your change.
I know the integration tests are not an easy read at the moment, so here is how you can fix the test.
I believe removing the 'service_name' => 'foo', entry should do the trick.
https://github.com/open-telemetry/opentelemetry-php-contrib/blob/main/tests/Integration/Symfony/OtelSdkBundle/DependencyInjection/OtelSdkExtensionTest.php#L338

The other way would be to add a serviceName to the MockExporter -> https://github.com/open-telemetry/opentelemetry-php-contrib/blob/main/tests/Integration/Symfony/OtelSdkBundle/Mock/SpanExporter.php
However I'm not really sure atm, if that would break any other tests.

[tidal]

Merging this, since the tests should be fixed with: #47