BRAKING refactor project structure.

Refactor: the project is now divided into a more clear structure, with **Infrastructure** and **Application** layers added.

Refactor: configurations are split into sections for different layers.

Fix: now EF Core related operations, such as migration, should be invoked in `OptixServe.Infrastructure`, with config file and data dir passed into `dotnet ef` command. See `OptixServe.Infrastructure/Utilites/DesignTimeDbContextFactory.cs` for details.

Fix: EF migrations are ignored in gitignore on purpose in early development.

OptixServe.Infrastructure/Data/DbInitializer.cs

@@ -0,0 +1,11 @@
+namespace OptixServe.Infrastructure.Data;
+
+public class DbInitializer(AppDbContext dbContext)
+{
+    private readonly AppDbContext _context = dbContext;
+
+    public void Initialize()
+    {
+        _context.Database.EnsureCreated();
+    }
+}