Add support for inline fragments

[rickschubert]

This library does not yet support GraphQL inline fragments. But this feature is supported by our "mirror library" json-to-graphql-query, see readme link on their project: https://github.com/vkolgi/json-to-graphql-query?tab=readme-ov-file#query-with-inline-fragments

We want to add support for inline fragments

Example syntax

{
  fieldName {
    ... on TypeName {
      field1
      field2
      # Additional fields specific to TypeName
    }
    ... on OtherTypeName {
      field3
      field4
      # Additional fields specific to OtherTypeName
    }
    # Additional fields common to all types
  }
}

Acceptance Criteria

• We have done our research on inline fragments and regarding their behaviour
• Our library supports inline fragments in a way that mirrors and complements our "partner" library json-to-graphql-query
• We have extensive tests to to prove the feature
• We have updated the readme as well as the readme example tests to highlight this new feature

---

(Initially brought up in the discussion on PR #23 , see here )