fix!: set AWS_ENDPOINT_URL_DEADLINE after installing service model

Main issue:

With the release of botocore that includes our service model, our method of configuring service model is no longer sufficient to contact endpoints other than the one included in botocore. We need to set AWS_ENDPOINT_URL_DEADLINE to tell boto that we want requests to Deadline Cloud to go to a different endpoint.

Small issues:

The test fixtures code that copies the service model from the test runner machine to the worker machine does not support gzip files, which is the format that service models included botocore are in.
The KEEP_WORKER_AFTER_FAILURE configuration was not working, workers are still shutting down after failing to start
The WORKER_REGION configuration is unnecessarily specific to the worker. The region can be applied to all components created by the test fixtures.

Set AWS_ENDPOINT_URL_DEADLINE whenever we install a service model
Support gzip (.json.gz) service model files
- The ServiceModel class was responsible for too many things. Removed the file paths and the AWS CLI commands from the class to simplify the code.
Make KEEP_WORKER_AFTER_FAILURE actually keep the worker around after failing
Deprecate WORKER_REGION and use REGION instead

hatch build && hatch run test
Installed this package into deadline-cloud-worker-agent and ran those integration tests (after making some fixes), verifying they succeed

Yes

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aws-deadline / deadline-cloud-test-fixtures