Generate a sample Vespa JSON payload given a Vespa tensor type

[cs195019]

Is your feature request related to a problem? Please describe.
Ability to have a JSON payload generator that prints a sample JSON payload given a tensor type. I think it would help a lot of us who are knew to the tensor data structures. For e.g.

generate_sample_json(tensor<float>(x[])); //prints out [1.0, 2.0, 3.0]

Describe the solution you'd like
The function can be defined in the Vespa tensor playground (or somewhere else) or a utility tensor function that I can use in the Vespa tensor playground website.

Describe alternatives you've considered
N/A

Additional context
N/A