Update API-Proxy manual build script

[damonbarry]

Update script to run from source root and behave the same for all supported architectures

Azure IoT Edge PR checklist:

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General Guidelines and Best Practices

• I have read the contribution guidelines.
• Title of the pull request is clear and informative.
• Description of the pull request includes a concise summary of the enhancement or bug fix.

Testing Guidelines

• Pull request includes test coverage for the included changes.
• Description of the pull request includes
  • concise summary of tests added/modified
  • local testing done.