[Rspamd] More explicit Sendgrid ID checking

data/conf/rspamd/lua/rspamd.local.lua

@@ -1,3 +1,10 @@
+-- Load sendgrid ID validator, thanks to https://github.com/fatalbanana
+local rspamd_util = require 'rspamd_util'
+local f = '/etc/rspamd/lua/ivm-sg.lua'
+if rspamd_util.file_exists(f) then
+  dofile(f)
+end
+
 rspamd_config.MAILCOW_AUTH = {
 	callback = function(task)
 		local uname = task:get_user()