Strongly Typed Content Item Converter does not support mapping name from an Option

### Motivation

When rendering a multiple choice elements in a strongly typed model, one must access the `List value` property of the [MultipleChoiceElement](https://github.com/Kentico/delivery-sdk-java/blob/master/delivery/src/main/java/com/kenticocloud/delivery/MultipleChoiceElement.java) class, which might be tedious. There should be a more straightforward path to the names of options.

One potential way to handle this would be like the following:
```java
@ContentItemMapping("product")
public class Product {
@ElementMapping("product_categories")
List productCategories;

//New feature
@ElementMappingOption(elementCodeName = "product_categories", optionCodeName = "footwear")
Boolean isFootwear;
}
```

### Original description

If an [Option](https://github.com/Kentico/delivery-sdk-java/blob/master/delivery/src/main/java/com/kenticocloud/delivery/Option.java) is mapped to a field, the name from the option should be used.

Start by reading MultipleChoiceElement.java and Option.java, then locate the strongly typed content item converter and its existing element-mapping tests. Verify how an Option is currently assigned to a field and define the expected name mapping for the proposed annotation; done means the example mapping works and existing conversion behavior remains intact.

Written by the indexing model from the issue text.