Do not ignore cloud_federation_api

Signed-off-by: Joas Schilling <coding@schilljs.com>

.gitignore

@@ -13,6 +13,7 @@
 # ignore all apps except core ones
 /apps*/*
 !/apps/accessibility
+!/apps/cloud_federation_api
 !/apps/comments
 !/apps/dav
 !/apps/files