Add ability for automatic URL path pattern discovery

When [the `use_path_as_transaction_name` config option](https://www.elastic.co/guide/en/apm/agent/java/current/config-http.html#config-use-path-as-transaction-name) is used, this can lead to transaction name explosion if path parameters are used. For this purpose, we also have [the `url_groups` config option](https://www.elastic.co/guide/en/apm/agent/java/current/config-http.html#config-url-groups), but it requires (possibly complex) user configuration.
By applying the algorithm presented [in this POC](https://github.com/eyalkoren/warehouse/tree/master/url-pattern-recognition/src/eyal/koren/url/recognition), the agent can auto-discover URL path patterns and use them as transaction names.

The additional advantage of implementing this now is that we will have the option of testing this algorithm, which we may want to employ in the future to facilitate head-based sampling.