Make use_path_as_transaction_name non-experimental

[felixbarny]

This option is present since the initial release. We should either work towards removing the experimental label or remove the feature.

Does anything speak against just removing the experimental label?

[felixbarny]

Another data point: the Node.js agent supports this option, too: https://www.elastic.co/guide/en/apm/agent/nodejs/current/configuration.html#use-path-as-transaction-name