Custom serializers should inherit generic types

[JaneWardSandy]

Generic update derived from #1276

@Get("{?pageable*}")
@ApiResponse(responseCode = "200")
suspend fun hello(pageable: Pageable): Page<String> = Page.of(listOf("Hello, World!"), pageable, 2)

interface SwaggerPage<T> {
  @get:Schema(description = "The content.") val content: List<T>
  @get:Schema(description = "The pageable for this slice.") val pageable: Pageable
}

Current the items type was object, which was lost the generic type

content:
  type: array
  description: The content.
  items:
    type: object

Expected it should be inherit the generic type if it had generics

content:
  type: array
  description: The content.
  items:
    type: string