[Test] Make it easier to deploy and invoke an unreleased version of ParallelCluster API

[gmarciani]

Description of changes

Make it easier to deploy and invoke an unreleased version of ParallelCluster API. In particular:

1. Make deployment script able to deploy an unreleased version of ParallelCluster API.
2. Improved the script to make a sample request to a deployed ParallelCluster API.

Developer Experience

To deploy an unreleased version of ParallelCluster API:

bash api/infrastructure/deploy-api.sh \
    --region us-east-1 \
    --stack-name PCAPI-3120-test \
    --s3-bucket my-bucket \
    --lambda-layer /path/to/lambda-layer-3.12.0-test.zip

Tests

Deployed and invoked both a released and an unreleased version of PCAPI.

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