Forcibly mark JSON Schema property as not required for a field of type Optional even if its @JsonProperty annotation has required = true

Event if field of type Optional has @JsonProperty annotation with required = true:

```java
public class Foo {
    @JsonProperty(required = true)
    public Optional<String> bar;
}
```
JSON Schema will forcibly mark its corresponding property as not required:

```json
{
    "type" : "object",
    "properties" : {
        "bar" : {
            "type" : "string"
        }
    }
}
```
instead of

```json
{
    "type" : "object",
    "properties" : {
        "bar" : {
            "type" : "string",
            "required" : true
        }
    }
}
```