Implement mechanism to throttle first create amplify call

[sobolk]

From #635 .

NPM runs into race condition on first attempt to use create amplify when NPX cache is not populated.

We should preserve ability for canary test to run scenarios that match customer behavior 1:1.
The PR, introduced a workaround to execute --help to hydrate npx cache.

The following alternatives should be considered in the long term:

1. Create a programatic component that throttles first call (not all of them) to npm create amplify.
   1. How does this run with multiple test files when each file runs as separate node process?
2. Farm out each test on separate worker ("generate test matrix" functionality)".

The alternative of just running test sequentially has been rejected as this makes runtime grow linearly with tests volume and doesn't scale.