Fix nginx failing to start on certain low-cache CPUs

roles/matrix-server/templates/nginx-conf.d/nginx-http.conf.j2

@@ -0,0 +1,5 @@
+# The default is aligned to the CPU's cache size,
+# which can sometimes be too low to handle our 2 vhosts (Synapse and Riot).
+#
+# Thus, we ensure a larger bucket size value is used.
+server_names_hash_bucket_size 64;