Add site setting to allow adding “content” to Discord messages

This can include ‘mentions’ such as `@everyone`

config/locales/server.en.yml

@@ -30,6 +30,7 @@ en:
     ########## DISCORD SETTINGS ###########
     #######################################
     chat_integration_discord_enabled: "Enable the Discord chat-integration provider"
+    chat_integration_discord_message_content: "The message to include above the summary when sending a notification to Discord"
     chat_integration_discord_excerpt_length: "Discord post excerpt length"
 
     #######################################

config/settings.yml

@@ -46,6 +46,8 @@ plugins:
 #######################################
   chat_integration_discord_enabled:
     default: false
+  chat_integration_discord_message_content:
+    default: ""
   chat_integration_discord_excerpt_length:
     default: 400
 

lib/discourse_chat/provider/discord/discord_provider.rb

@@ -36,6 +36,7 @@ module DiscourseChat
         end
 
         message = {
+          content: SiteSetting.chat_integration_discord_message_content,
           embeds: [{
             title: post.topic.title,
             description: post.excerpt(SiteSetting.chat_integration_discord_excerpt_length, text_entities: true, strip_links: true, remap_emoji: true),