added required nuget package to enable serilog based centralized logging in gelf format

[excelite]

Changes

• added the nuget package to enable Serilog's GELF logging.

Issues
none

feature requests
Add support for centralized logging

example configuration
/config/logging.json

{
    "Serilog": {
        "MinimumLevel": "Information",
        "WriteTo": [
            {
                "Name": "Console",
                "Args": {
                    "outputTemplate": "[{Timestamp:HH:mm:ss}] [{Level:u3}] {Message:lj}{NewLine}{Exception}"
                }
            },
            {
                "Name": "Graylog",
                "Args": {
                    "HostnameOrAddress": "localhost",
                    "Port": "12202",
                    "TransportType": "Udp"
                }
            }
        ]
    }
}

alternative valid values:
HostnameOrAddress can also be an IP Address like:
"192.0.0.1"
TransportType can also be one of these:
"Tcp", "Http"

background
The logging in Jellyfin is quite messy (read: non-uniform). This includes two Jellyfin modules logging to .txt files and the others to .log files. Also some modules use the more advanced way of enriching the log messages in a more "structured data" like way, while others don't.

I think it would be a nice way to start a cleanup of the logger with easy way to evaluate the results.