How will the user enable new keys on the form? Will there be a dropdown or some ui for them to pick new key/value pairs to add?
If you choose to use our native form component, you'll want to add all possible child components and then you can show/hide them dynamically based on what the user selects.
Otherwise, you could use our JSON schema form, and you could have a dynamic form schema that changes based on user input (using Javascript inside of double curly brackets {{}})