Theia: fix installation
This addresses both : - some random failures we sometimes have when installing `python-language-server` fail - caddy no longer being installed here since nexedi/slapos!821 See merge request nexedi/slapos!828
This addresses both : - some random failures we sometimes have when installing `python-language-server` fail - caddy no longer being installed here since nexedi/slapos!821 See merge request nexedi/slapos!828