MINOR: quic: Tunable "max_idle_timeout" transport parameter

Add two tunable settings both for backends and frontends "max_idle_timeout"
QUIC transport parameter, "tune.quic.frontend.max-idle-timeout" and
"tune.quic.backend.max-idle-timeout" respectively.
cfg_parse_quic_time() has been implemented to parse a time value thanks
to parse_time_err(). It should be reused for any tunable time value to be
parsed.
Add the documentation for this tunable setting only for frontend.
diff --git a/src/haproxy.c b/src/haproxy.c
index 203897b..a112c23 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -115,6 +115,7 @@
 #include <haproxy/namespace.h>
 #include <haproxy/net_helper.h>
 #include <haproxy/openssl-compat.h>
+#include <haproxy/quic_tp-t.h>
 #include <haproxy/pattern.h>
 #include <haproxy/peers.h>
 #include <haproxy/pool.h>
@@ -205,6 +206,8 @@
 		.idle_timer = 1000, /* 1 second */
 #endif
 #ifdef USE_QUIC
+		.quic_backend_max_idle_timeout = QUIC_DFLT_BACK_MAX_IDLE_TIMEOUT,
+		.quic_frontend_max_idle_timeout = QUIC_DFLT_FRONT_MAX_IDLE_TIMEOUT,
 		.quic_retry_threshold = QUIC_DFLT_RETRY_THRESHOLD,
 		.quic_streams_buf = 30,
 #endif /* USE_QUIC */