Set content types settings on mastofe endpoint.

lib/pleroma/web/mastodon_api/mastodon_api_controller.ex

@@ -1128,7 +1128,8 @@ def index(%{assigns: %{user: user}} = conn, _params) do
           compose: %{
             me: "#{user.id}",
             default_privacy: user.info.default_scope,
-            default_sensitive: false
+            default_sensitive: false,
+            allow_content_types: Config.get([:instance, :allowed_post_formats])
           },
           media_attachments: %{
             accept_content_types: [