generate input objects, start using Nullable

[davidbloss]

Resolves #573

🚨 This PR contains BREAKING CHANGES for the upcoming v2025 opslevel-go release 🚨

Run task gen to see new code generated in input.go

Noteworthy Changes

• ❗The *Nullable[<type>] type now wraps optional fields of most structs in input.go. This sweeping change enables setting input object fields to JSON null, resolves ambiguity during API update calls, and completes a planned major refactor before the next major release of opslevel-go.
• In scalar.go, a new UnmarshalJSON() for Nullable types was added to correctly unmarshal JSON values to this custom type.
• task gen now uses the template in templates/inputObjects.tpl to generate everything in input.go
• In gen.go: enumExamples, listExamples, and scalarExamples are used to set values in example: struct tags
• All RefOf() calls have been replaced with NewNullableFrom()
• Tests have been updated that verify these changes.

Checklist

• I have run this code, and it appears to resolve the stated issue.
• This PR does not reduce total test coverage
• This PR has no user interface changes or has already received approval from product management to change the interface.
• Does this change require a Terraform schema change?
  • If so what is the ticket or PR #
• Make a changie entry that explains the customer facing outcome of this change

[rocktavious]

missed?

[rocktavious]

🚀