Add config circuit-breaker for heroes calculations during sync.

Signed-off-by: Jason Volk <jason@zemos.net>

tuwunel-example.toml

@@ -1136,6 +1136,17 @@
 #
 #push_everything = false
 
+# Setting to false disables the heroes calculation made by sliding and
+# legacy client sync. The heroes calculation is mandated by the Matrix
+# specification and your client may not operate properly unless this
+# option is set to true.
+#
+# This option is intended for custom software deployments seeking purely
+# to minimize unused resources; the overall savings are otherwise
+# negligible.
+#
+#calculate_heroes = true
+
 # Allow local (your server only) presence updates/requests.
 #
 # Note that presence on tuwunel is very fast unlike Synapse's. If using