Add: binding setting file items to `AppSettings` class so to provide DI access as `IOptions<OptixServeSettings>`.
Add: EF Core and DbContext to access database in services. This results in disabling NativeAOT due to poor supports for *pre-compiled query*, however many design are optimized for AOT for later re-adoption.
Add: `DesignTimeDbContextFactory` to support EF Core migrations in NativeAOT. (Kept for re-enabling AOT.)
Add: `DbInitializer` for ensuring database connecting in startup.
Add: `ConfigurationHelper.CreateDefaultBuilder()` to read configuration files in default locations. Note this method is currently ONLY used by `DesignTimeDbContextFactory`. Refactor is expected.
Add: `CommonErrorDto` for simple error message.
Add: `VersionEndpoint` ONLY for debugging and testing purpose. Verylikely to be removed in the future.
Other: many utilities and fixes easy to understand.
Note: EF Core migrations are excluded in the early development. Not expected to be added in version control before v1.0 beta.
Fix: re-implement `UserEndpoint` as static style which works best with minimal API, simplify the DI framework.
Fix: remove no needed service register in main program.
**Note: This implementation is not in minimalAPI way and not optimized, expected to be changed soon.**
Add: `UserService` and its interface `IUserService`.
Fix: `UserEndpoint` is now in instance class style with DI to work.
Fix: change main program to work with above design.
