Merge pull request #246117 from Ralith/fix-synapse-well-known-example

  clientConfig."m.homeserver".base_url = baseUrl;

  serverConfig."m.server" = "${fqdn}:443";

  mkWellKnown = data: ''

    add_header Content-Type application/json;

    default_type application/json;

    add_header Access-Control-Allow-Origin *;

    return 200 '${builtins.toJSON data}';

  '';