MINOR: quic_stats: Add a new stats module for QUIC

This is a very minimalist frontend only stats module with only one gauge for the
QUIC establishing connections count.
diff --git a/Makefile b/Makefile
index 56fd89a..918ddc1 100644
--- a/Makefile
+++ b/Makefile
@@ -637,7 +637,7 @@
                 src/quic_frame.o src/quic_cc.o src/quic_cc_newreno.o src/mux_quic.o \
                 src/cbuf.o src/qpack-dec.o src/qpack-tbl.o src/h3.o src/qpack-enc.o \
                 src/hq_interop.o src/cfgparse-quic.o src/quic_loss.o \
-                src/quic_stream.o
+                src/quic_stream.o src/quic_stats.o
 endif
 
 ifneq ($(USE_LUA),)