refactor!: improve support for ec2 instance workers

What was the problem/requirement? (What/Why)

The PosixInstanceWorker and WindowsInstanceWorker classes implement a CMF Worker based on an ec2 host. In both cases they start with an empty AMI image (AL2023 or Win Server 2022) then set up users, install the agent, etc. Tests that need to use an AMI that already has users and the agent installed end up having to hack around a lot of assumptions in these classes, or reimplement everything for an ec2-based worker from scratch.

What was the solution? (How)

Refactor the PosixInstanceWorker and WindowsInstanceWorker to split them into os-specific base classes that contain all of the generic worker implementation stuff (starting the worker, getting its id, etc), and a derived class that implements the user-setup, agent install, and the like. This makes space for tests that use an AMI with the users & agent pre-setup to derive from the os-specific base classes to get the generic ec2-worker test functionality.

What is the impact of this change?

Downstream consumers no longer need to resort to hacky workarounds to test worker configurations that have the agent & host setup baked into an AMI

How was this change tested?

I've run this with the deadline-cloud-worker-agent e2e tests; the windows & linux e2e tests, and the cross-os tests under each.

I've also run this against internal testing infrastructure that is providing a pre-built AL2023 and WindowsServer2022 AMI to the testing infrastructure.

Everything passes everywhere. The deadline-cloud-worker-agent e2e tests need no modifications to take on these changes.

Was this change documented?

Is this a breaking change?

BREAKING CHANGE: PosixInstanceWorker has been renamed to PosixInstanceBuildWorker, and WindowsInstanceWorker has been renamed to WindowsInstanceBuildWorker.

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aws-deadline / deadline-cloud-test-fixtures