Allow caller to disable Mariner arm64 build

The Mariner arm64 build is currently failing. When it builds identity service bits, it tries to populate the version by getting the latest 1.5. tag from the identity service repo. There are no 1.5. tags yet, so it sends an empty version which causes make to fail.

The root cause is that we bumped our release version in code much sooner than we normally do (i.e., the period of time between bumping the version in code and actually publishing the bits is usually hours, but this time it's a couple weeks). The problem will resolve automatically once we release, and we don't release Mariner arm64 externally, so we'll simply disable it now, and re-enable as soon as we release.

To test, I ran the CI Build pipeline and confirmed it passes and Mariner arm64 is skipped.

Azure IoT Edge PR checklist:

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

Testing Guidelines

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

Azure / iotedge