Hacktoberfest - TcpSlaveAgentListener optimization (#5012)

* TcpSlaveAgentListener.ConnectionHandler.run: Move allocation of output Writer to error method

* TcpSlaveAgentListener.ConnectionHandler.error: Replace PrintWriter to DataOutputStream

* TcpSlaveAgentListener.ConnectionHandler.respondHello: Replace OutputStreamWriter by DataOutputStream to avoid allocation of big buffer

* TcpSlaveAgentListener.ConnectionHandler.run: Replace Charsets to StandardCharsets

* TcpSlaveAgentListener.ConnectionHandler: Fix encoding of response

* TcpSlaveAgentListener: Remove unused imports

Co-authored-by: Ilya Gulyaev <ilya.gulyaev@nordigy.ru>