Fix path to required version data

[crutchfield]

🗣 Description

Identify module base dir and get RequirementVersions.ps1 relative to that instead of relying on $PSScriptRoot
closes #968

💭 Motivation and context

Initialize-SCuBA was failing to find RequiredVersions.ps1 when executed from a owrkflow running.

🧪 Testing

• Ran Invoke-SCuBA from repo root
• Ran Invoke-SCuBA from home directory
• Ran Invoke-SCuBA from "Nightly Product Test" workflow on a runner.

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[schrolla]

Tested fix by running Initialize-SCuBA from the checkout repo directory, from its grandparent directory, and reviewing the nightly testing action taken previously. Also ran Invoke-SCuBA to ensure it ran as expected and it did.
Code review shows update to ModuleBaseDir as a solid location from which to base calculation of the RequiredVersions.ps1 relative script location. See requested change below for minor updates for it to function properly in workflow scenarios.

[james-garriss]

Please add the catch while you're there, something like this:

    if (Test-Path -Path $RequiredModulesPath) {
        . $RequiredModulesPath
    }
    else {
        Write-Error "Unable to find required modules path at $RequiredModulesPath"
    }

[james-garriss]

Thanks for good work.

[schrolla]

Updated code works when tested in both the expected and error condition cases. Ran Invoke-Scuba successfully on test tenant and ran Initialize-SCuBA successfully. Renamed RequiredVersions.ps1 and ran again and received expected error condition. Looks good to me.

[crutchfield]

@nanda-katikaneni PR is ready to merge to main. Smoke test failure unrelated to PR.