User-friendly error when test name is not set in cloud execution

[na--]

Cloud execution of tests via k6 cloud requires that the test's name is set. That can be done via the ext.loadimpact.name property in the script's exported options (or global JSON config), or via the K6_CLOUD_NAME environment variable. If none of those values are set, the script filename is used instead.

But when passing test scripts via stdin (which is very common when using docker: docker run -e K6_CLOUD_TOKEN="<my-cloud-token>" -i loadimpact/k6 cloud - <script.js), k6 doesn't know the filename, and this results in confusing errors like Unexpected HTTP error from https://ingest.loadimpact.com/v1/archive-upload: 422 Unprocessable Entity.

We should validate that the script's name property is set in k6, before sending the archive bundle to the cloud, and emit a user-friendly error that suggests that users should set K6_CLOUD_NAME or ext.loadimpact.name

[robingustafsson]

We've fixed this issue at least two times in the past (#214, #510), it's time for a test case 😄

I think we should have a default name when the script comes from stdin (if not we default to the filename), as we've had in the past, and at most warn/inform the user with a friendly message that they can set their own name by setting it in the JS options or using the env var (we can detect it in Insights and hint there as well).