Provide a more human-friendly error message when APPLURA_DEPLOY_KEY is not set or is not valid

[gabesullice]

The current error output is:

Run applura/deploy@1.0.1
file:///home/runner/work/_actions/applura/deploy/1.0.1/dist/index.js:57825
      throw new UnknownError(`unexpected status code: ${response.status}`);
            ^

UnknownError: unexpected status code: 401
    at DeployKey.getProject (file:///home/runner/work/_actions/applura/deploy/1.0.1/dist/index.js:57825:13)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async apiDeploy (file:///home/runner/work/_actions/applura/deploy/1.0.1/dist/index.js:58027:19)

The solution to this error message is to provide a valid deploy key as a GitHub actions repository secret named APPLURA_DEPLOY_KEY