Change MediaProduct.extras type

[subhasha1]

Changed from: Map<String, String?>?
Changed to: Map<String, Extra?>?.

Extra is defined as:

sealed interface Extra {
    data class Bool(val value: Boolean) : Extra
    data class Number(val value: kotlin.Number) : Extra
    data class Text(val value: String) : Extra
    data class CollectionList(val value: List<Extra>?) : Extra
    data class CollectionMap(val value: Map<String, Extra?>?) : Extra
}

This enables support for more dynamic types and not limited to map of String values.

To support conversion to and from JSON, custom JsonSerializer and JsonDeserializer for Extra are added.