Add check to ensure OPA executable is available

[adhilto]

💡 Summary

Before attempting to execute OPA, first check to ensure the executable is available and at least the minimum version, and provide a helpful error message if not.

Motivation and context

If you try running ScubaGoggles without the executable, the error message does not provide the user with actionable information.

Implementation notes

See #410.

Acceptance criteria

• Check to see if executable is present is implemented
• Check to see if acceptable version is implemented
• Error message contains actionable information