Runner Incept test for fleeting AWS plugin

The AWS Fleeting plugin needs end-to-end testing to confirm the plugin is loading:

• https://gitlab.com/gitlab-org/fleeting/fleeting-plugin-aws covered in gitlab-org/ci-cd/tests/runner-incept!41 (merged)

Things that worked stop working when we fix things that weren't working. Engineering whack-a-mole.

Related issue to get ideas for testing scenarios: #29436 (closed)

A note from @ajwalker on a possible approach:

I was thinking that we’d have a public testing package in fleeting which runs through various scaling scenarios, testing basic functionality etc.

Each plugin would them import this package and call a function to kick off the the integration test suite. I figured this would would be against real cloud providers, so we’d create a sandbox account for GCP and AWS.