Fix handling of @InputArgument for Java objects with optionals.

[srinivasankavitha]

Pull Request type

• [x] Bugfix
• [ ] Feature
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Other (please describe):

Changes in this PR

This PR fixes handling of @InputArgument for optionals. The current implementation of the DefaultInputObjectMapper does not handling converting from map to optionals, resulting in the following error when used:

**Failed to convert from type [java.util.LinkedHashMap<?, ?>] to type [@com.netflix.graphql.dgs.InputArgument 

Conversion of String to Optional, for e.g works fine since Spring's ObjectToOptionalConverter handles this fine: https://github.com/spring-projects/spring-framework/blob/main/spring-core/src/main/java/org/springframework/core/convert/support/ObjectToOptionalConverter.java

Adding similar logic to the DefaultInputObjectMapper to handle optionals based on this code: https://github.com/spring-projects/spring-framework/blob/main/spring-core/src/main/java/org/springframework/core/convert/support/ObjectToOptionalConverter.java#L76

Describe the new behavior from this PR, and why it's needed Issue #1925

[filippocozzini]

Any update?

[srinivasankavitha]

Any update?

Sorry for the delay. I need to address some of the comments before I can push the fix through.

[srinivasankavitha]

Declining this PR in favor of a better fix here: https://github.com/Netflix/dgs-framework/pull/1951