[Enhancement] Change the default behavior of @EnableDubboConfig.multiple()

The default value of `@EnableDubboConfig#multiple()` method attribute is `false`, and it will be changed to `true`, thus single and multiple configuration bindings work at the same time, e.g:

```properties
# Single configuration binding
dubbo.protocol.name=dubbo
# Multiple configuration binding
dubbo.protcols.rest.name = rest
```