Suggestion: add random data generation helpers

Hey folks,
awesome tool you wrote here!

As I use the tool for setting up demo data for my projects, I would find it cool to have a small set of helpers to e.g. create a random email or a random alphanumeric user name.

Those helpers could be used like:

# Create a new doggy thing with JSON body:
POST https://example.org/api/dogs
{
    "id": 0,
    "name": "{{random_alphanumeric(12)}}",
    "picture": "images/scottish-terrier.jpeg",
    "age": {{random_int()}},
    "breed": "Scottish Terrier",
    "location": "Lisco, Alabama"
}

I know that I could use the --variables functionality to inject variables and generate the random data outside of hurl, but I think this could come in handy for having self-contained .hurl - files.

If you like this idea or have more input, I would be happy to contribute the code myself! I wanted to let you guys know first and discuss it before I go for it!

Best regards
Stefan

Start by reviewing the existing --variables functionality and how .hurl files process template expressions. Define the supported random helpers and their output constraints, then determine the tests needed for examples such as random_alphanumeric(12) and random_int(); done means the helpers work in self-contained .hurl files.