Streamline startup code

[Bond-009]

Before without web dir set:

[18:58:57] [INF] [1] Main: Jellyfin version: 10.8.0
[18:58:57] [INF] [1] Main: Environment Variables: ["[DOTNET_CLI_TELEMETRY_OPTOUT, 1]", "[DOTNET_ROOT, /home/bond/dotnet]", "[ASPNETCORE_URLS, http://localhost:8096]", "[JELLYFIN_LOG_DIR, /home/bond/.local/share/jellyfin/log]", "[ASPNETCORE_ENVIRONMENT, Development]"]
[18:58:57] [INF] [1] Main: Arguments: ["/home/bond/dev/jellyfin/Jellyfin.Server/bin/Debug/net6.0/jellyfin.dll"]
[18:58:57] [INF] [1] Main: Operating system: Linux
[18:58:57] [INF] [1] Main: Architecture: X64
[18:58:57] [INF] [1] Main: 64-Bit Process: True
[18:58:57] [INF] [1] Main: User Interactive: True
[18:58:57] [INF] [1] Main: Processor count: 16
[18:58:57] [INF] [1] Main: Program data path: /home/bond/.local/share/jellyfin
[18:58:57] [INF] [1] Main: Web resources path: /home/bond/dev/jellyfin/Jellyfin.Server/bin/Debug/net6.0/jellyfin-web
[18:58:57] [INF] [1] Main: Application directory: /home/bond/dev/jellyfin/Jellyfin.Server/bin/Debug/net6.0/
[18:58:57] [INF] [1] Emby.Server.Implementations.AppBase.BaseConfigurationManager: Setting cache path: /home/bond/.cache/jellyfin
[18:58:57] [FTL] [1] Main: Error while starting server.
System.InvalidOperationException: The server is expected to host the web client, but the provided content directory is either invalid or empty: /home/bond/dev/jellyfin/Jellyfin.Server/bin/Debug/net6.0/jellyfin-web. If you do not want to host the web client with the server, you may set the '--nowebclient' command line flag, or set'hostwebclient=false' in your config settings.
   at Jellyfin.Server.Program.StartApp(StartupOptions options) in /home/bond/dev/jellyfin/Jellyfin.Server/Program.cs:line 179
[18:58:57] [INF] [1] Main: Running query planner optimizations in the database... This might take a while
[18:58:57] [FTL] [1] Main: Unhandled Exception
System.ArgumentNullException: Value cannot be null. (Parameter 'provider')
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
   at Emby.Server.Implementations.ApplicationHost.Resolve[T]() in /home/bond/dev/jellyfin/Emby.Server.Implementations/ApplicationHost.cs:line 415
   at Jellyfin.Server.Program.StartApp(StartupOptions options) in /home/bond/dev/jellyfin/Jellyfin.Server/Program.cs:line 227
   at Jellyfin.Server.Program.<Main>(String[] args)
Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'provider')
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
   at Emby.Server.Implementations.ApplicationHost.Resolve[T]() in /home/bond/dev/jellyfin/Emby.Server.Implementations/ApplicationHost.cs:line 415
   at Jellyfin.Server.Program.StartApp(StartupOptions options) in /home/bond/dev/jellyfin/Jellyfin.Server/Program.cs:line 227
   at Jellyfin.Server.Program.<Main>(String[] args)

After:

[18:49:27] [INF] [1] Main: Jellyfin version: 10.8.0
[18:49:27] [INF] [1] Main: Environment Variables: ["[ASPNETCORE_URLS, http://localhost:8096]", "[ASPNETCORE_ENVIRONMENT, Development]", "[JELLYFIN_LOG_DIR, /home/bond/.local/share/jellyfin/log]", "[DOTNET_ROOT, /home/bond/dotnet]", "[DOTNET_CLI_TELEMETRY_OPTOUT, 1]"]
[18:49:27] [INF] [1] Main: Arguments: ["/home/bond/dev/jellyfin/Jellyfin.Server/bin/Debug/net6.0/jellyfin.dll"]
[18:49:27] [INF] [1] Main: Operating system: Linux
[18:49:27] [INF] [1] Main: Architecture: X64
[18:49:27] [INF] [1] Main: 64-Bit Process: True
[18:49:27] [INF] [1] Main: User Interactive: True
[18:49:27] [INF] [1] Main: Processor count: 16
[18:49:27] [INF] [1] Main: Program data path: /home/bond/.local/share/jellyfin
[18:49:27] [INF] [1] Main: Web resources path: /home/bond/dev/jellyfin/Jellyfin.Server/bin/Debug/net6.0/jellyfin-web
[18:49:27] [INF] [1] Main: Application directory: /home/bond/dev/jellyfin/Jellyfin.Server/bin/Debug/net6.0/
[18:49:27] [ERR] [1] Main: The server is expected to host the web client, but the provided content directory is either invalid or empty: /home/bond/dev/jellyfin/Jellyfin.Server/bin/Debug/net6.0/jellyfin-web. If you do not want to host the web client with the server, you may set the '--nowebclient' command line flag, or set'hostwebclient=false' in your config settings.
[18:49:27] [INF] [2] Main: Received a SIGTERM signal, shutting down