[MEV Boost\Builder] Response Body not closed (OkHttp)

[StefanBratanov]

The following warning was shown to one of our users.

consensus_1         | Jun 09, 2022 2:37:48 PM okhttp3.internal.platform.Platform log
consensus_1         | WARNING: A connection to http://mev-boost:18550/ was leaked. Did you forget to close a response body? To see where this was allocated, set the OkHttpClient logger level to FINE: Logger.getLogger(OkHttpClient.class.getName()).setLevel(Level.FINE);
consensus_1         | Jun 09, 2022 2:37:48 PM okhttp3.internal.platform.Platform log
consensus_1         | WARNING: A connection to http://mev-boost:18550/ was leaked. Did you forget to close a response body? To see where this was allocated, set the OkHttpClient logger level to FINE: Logger.getLogger(OkHttpClient.class.getName()).setLevel(Level.FINE);

This warning is due to the fact the ResponseBody in OkHttpRestClient is not closed and it must be.