* Forces the AL2 build container image for fixtures that depend on it,
via `engines.node` in package.json for most cases.
* The `testDeployment()` function was updated to send
`projectSettings.nodeVersion` in the POST body, to mimic the behavior in
CLI.
* For Go, Ruby, and Python tests, the `projectSettings.nodeVersion`
property is set "globally" in the Jest setup file, so that individual
fixtures didn't need to be adjusted.
Previously, our test fixtures used to use a probes prop in `vercel.json` that was removed right before it was deployed.
This PR allows a separate `probes.json` file with the same content to separate the test fixture input from the test probes.
This allows us to test real "zero config" deployments without a `vercel.json` file.
