core.certmanager: Lower severity for tls config not having cert
This is needed for SNI where certificates are in separate
per-hostname contexts, not the main one.
If there is a cert, it will still require a corresponding key.
For full information on our dependencies, version requirements, and
where to find them, see https://prosody.im/doc/depends
If you have luarocks available on your platform, install the following:
- luaexpat
- luasocket
- luafilesystem
- luasec