chore: Add validation to prevent message flooding (#9254)

- Add a validation to limit messages created per minute to avoid message flooding cases.

lib/limits.rb

@@ -4,4 +4,8 @@ module Limits
   URL_LENGTH_LIMIT = 2048 # https://stackoverflow.com/questions/417142
   OUT_OF_OFFICE_MESSAGE_MAX_LENGTH = 10_000
   GREETING_MESSAGE_MAX_LENGTH = 10_000
+
+  def self.conversation_message_per_minute_limit
+    ENV.fetch('CONVERSATION_MESSAGE_PER_MINUTE_LIMIT', '200').to_i
+  end
 end