refactor: reuse default SerializerOptions in Minimal APIs

[cnblogs-dudu]

Avoid Chinese characters being encoded

[ikesnowy]

I revert all your changes under /src and the test you added can still be passed, please provide a valid test.

[ikesnowy]

Make the DefaultJsonSerializerOptions nullable seems reasonable and still remain configurability.

public JsonSerializerOptions? DefaultJsonSerializerOptions { get; set; }

Some old application may use PascalCase for JSON serialization and that breaks communication between new and old apps that using the Architecture.

Making serialization option configurable makes it possible to fix on the old application side without changing the global JSON serialization options.

I could make the change if that's okay with you.

[cnblogs-dudu]

It turned out there was a really simple approach.

public JsonSerializerOptions DefaultJsonSerializerOptions { get; set; } = new JsonOptions().SerializerOptions;