API: Add APIHandler back

This handler should no have been removed in 4276, as it adds the required CORS
header (Access-Control-Allow-Origin) for public acces to the API.

Thanks to iBicha for noticing this!

src/invidious.cr

@@ -217,6 +217,7 @@ public_folder "assets"
 
 Kemal.config.powered_by_header = false
 add_handler FilteredCompressHandler.new
+add_handler APIHandler.new
 add_handler AuthHandler.new
 add_handler DenyFrame.new
 add_context_storage_type(Array(String))