fix: any handler sets a default application/json #3103

Loadtest Results

param	main	head	v12.0.0
bytes_in.mean	1030.3450859252946	1030.2697583049778	1030.4028602551039
bytes_in.total	29018639	29369900	29324235
bytes_out.mean	3848.092351938645	3849.3096432455186	3848.3658947960225
bytes_out.total	108377673	109732270	109520645
duration	60001431457	60001480507	60013084022
errors.0	400 Bad Request	400 Bad Request	400 Bad Request
latencies.50th	923868	918978	919572
latencies.90th	2780683	1996972	2081226
latencies.95th	13898051	13678388	13611962
latencies.99th	14169122	13900064	13974326
latencies.max	24665175	25233472	25243089
latencies.mean	2129480	2103781	2107801
latencies.min	153096	152524	156041
latencies.total	59974685408	59972504853	59985935954
rate	469.38880150190613	475.1049433967595	474.21325638867864
requests	28164	28507	28459
status_codes.200	15363	15549	15524
status_codes.201	2560	2592	2587
status_codes.204	7680	7774	7761
status_codes.400	2561	2592	2587
success	0.9090683141599201	0.9090749640439191	0.909097297867107
throughput	426.70069434227094	431.8989428585419	431.09986822524235
wait	814472	981709	852207