[BitSail][Feature] FakeSource supports nullable

[kyle-hawk]

Describe the solution you'd like

Subtask of https://github.com/bytedance/bitsail/issues/243

Fake Connector not be able to declare whether the field is nullable, this can be useful sometimes

maybe it can be conf like this in the future

        {
               "name": "double_field",
               "type": "double",
               "nullable": false
        }

[liuxiaocs7]

I remember that settings are reserved in TypeInfo. I'm not sure whether they can be set there?

https://github.com/bytedance/bitsail/blob/fbc5d22e1901f86a54cd388967629541a1a51739/bitsail-common/src/main/java/com/bytedance/bitsail/common/typeinfo/TypeInfo.java#L22-L40