chore(windows): fortify build scripts against environment leaks and silent crashes

[Piyush0049]

While working with the Windows build scripts, I noticed several areas where terminating exceptions (like a failing Docker build or a crashing Pester test) would bypass cleanup logic. This leaves temporary files on disk and leaks global environment variables into the developer session, which can silently hijack subsequent local builds.

This PR does the following:

1. Prevents Env Leaks: Wraps $env:WINDOWS_VERSION_OVERRIDE, $env:DOCKERHUB_ORG_REPO, and $env:CONTROLLER_TAG in try/finally blocks so they are guaranteed to be cleaned up or restored even if the build or Invoke-Pester crashes.
2. Fixes Get-SutImage Crash: Swaps Resolve-Path for Join-Path to prevent raw ItemNotFoundException crashes, allowing the script intended friendly error message to actually render.
3. Strict-Mode Safety: Wraps docker exec in Get-JenkinsPassword in a try/catch block to ensure forward compatibility with PS 7.3+ native command error preferences.
4. Temp File Cleanup: Ensures Build-DockerChild deletes Dockerfile-windows.tmp in a finally block if the build fails.

Related Issues

Fixes #2413
Fixes #2414

Testing done

• Simulated environment leaks by throwing exceptions inside the Invoke-Pester block and verified the finally blocks successfully cleaned up $env:DOCKERHUB_ORG_REPO and $env:CONTROLLER_TAG.
• Simulated missing Dockerfiles to verify Get-SutImage now correctly outputs the friendly string error rather than crashing the script.
• Verified that strict-mode terminating errors inside Get-JenkinsPassword are safely caught and return $null as intended.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[lemeurherve]

@Piyush0049 can you open an issue per type of problem you see so we can discuss it before opening any pull request please? It would greatly help us evaluate them before acting if needed.

[Piyush0049]

@Piyush0049 can you open an issue per type of problem you see so we can discuss it before opening any pull request please? It would greatly help us evaluate them before acting if needed.

Sure, I would open issue before opening a PR from next time. I am opening the issues related to this PR.