Change mechanism for calling PSSA

[james-garriss]

🗣 Description

Previously, the pipelines had been calling PSScriptAnalyzer using MegaLinter. This change uses PowerShell code that installs the PSSA module install and runs PSSA against every PowerShell file.

💭 Motivation and context

Closes: #1366

🧪 Testing

Ran CI pipeline.
Added "Write-Host" code to trigger failures.
Added a debugging line to verify which files are tested.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• PR targets the correct parent branch (e.g., main or release-name) for merge.
• Changes are limited to a single goal - eschew scope creep!
• Changes are sized such that they do not touch excessive number of files.
• These code changes follow the ScubaGear [content style guide]
• Related issues these changes resolve are linked preferably via [closing keywords]
• All relevant type-of-change labels added.
• All relevant project fields are set.
• All relevant repo and/or project documentation updated to reflect these changes.
• All automated checks (e.g., linting, static analysis, unit/smoke tests) passed.

✅ Pre-merge checklist

• PR passed smoke test check.
• Feature branch has been rebased against changes from parent branch, as needed
• Resolved all merge conflicts on branch
• Notified merge coordinator that PR is ready for merge via comment mention

✅ Post-merge checklist

• Feature branch deleted after merge to clean up repository.
• Verified that all checks pass on parent branch (e.g., main or release-name) after merge.