feat: option to restrict Discord auth to a specific server (#1548)

* Optionally restrict discord authentication to members of a specific server

* fix: discord auth module code linting

Co-authored-by: Lucas Neves <lneves@modusgames.com>
Co-authored-by: Nicolas Giard <github@ngpixel.com>

server/modules/authentication/discord/definition.yml

@@ -18,3 +18,8 @@ props:
     title: Client Secret
     hint: Application Client Secret
     order: 2
+  guildId:
+    type: String
+    title: Server ID
+    hint: Optional - Your unique server identifier, such that only members are authorized
+    order: 3