Add sends_allowed config setting

This provides global control over whether users can create Bitwarden Sends.

.env.template

@@ -56,6 +56,11 @@
 # WEBSOCKET_ADDRESS=0.0.0.0
 # WEBSOCKET_PORT=3012
 
+## Controls whether users are allowed to create Bitwarden Sends.
+## This setting applies globally to all users.
+## To control this on a per-org basis instead, use the "Disable Send" org policy.
+# SENDS_ALLOWED=true
+
 ## Job scheduler settings
 ##
 ## Job schedules use a cron-like syntax (as parsed by https://crates.io/crates/cron),