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/Configuration/InfrastructureConfiguration.cs

@@ -0,0 +1,18 @@
+namespace OptixServe.Infrastructure.Configuration;
+
+public record InfrastructureConfiguration
+{
+    public DatabaseSettings? Database { get; set; } = new();
+}
+
+public enum DatabaseType
+{
+    Sqlite,
+    MySQL
+}
+
+public record DatabaseSettings
+{
+    public DatabaseType Type { get; set; } = DatabaseType.Sqlite;
+    public string? Host { get; set; }
+}