Use random salt for each fingerprint key

Salt length depended on fingerprint name length, which lead to weak salts in some cases
It's now a fixed length (12 bytes)

Akari.Prototype.Server/Program.cs

@@ -2,6 +2,7 @@ using Akari.Prototype.Server.Cli.Commands;
 using Akari.Prototype.Server.Options;
 using Akari.Prototype.Server.Utils.Extensions;
 using CliFx;
+using Isopoh.Cryptography.Argon2;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;