Major: support for .NET 9 (#26)

* Updated target to net9.0

* Merged net8.0 and net9.0 targets

* Updated workflows

.devcontainer/devcontainer.json

@@ -3,7 +3,7 @@
 {
 	"name": "SimpleOTP",
 	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
-	"image": "mcr.microsoft.com/devcontainers/dotnet:1-8.0",
+	"image": "mcr.microsoft.com/devcontainers/dotnet:1-9.0",
 
 	// Features to add to the dev container. More info: https://containers.dev/features.
 	// "features": {},