provisioner/powershell: add -NonInteractive to default commands

[VedantMadane]

Description

Add -NonInteractive flag to all default powershell and pwsh invocations in the PowerShell provisioner's defaultExecuteCommand() and defaultScriptCommand() methods.

Packer builds are inherently non-interactive. When a PowerShell command unexpectedly prompts for user input (e.g., a confirmation dialog from Install-Module), the build hangs indefinitely with no indication of what went wrong. The -NonInteractive flag causes PowerShell to immediately throw a terminating error instead of waiting for input, which lets operators diagnose and fix the issue.

The flag is only added when execution_policy is not none -- when execution policy is none, the default command string contains no powershell/pwsh prefix, so there is nothing to attach the flag to.

All existing unit tests have been updated to expect the new flag in the generated command strings.

Resolved Issues

Closes #12637

Rollback Plan

If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

No changes to security controls.

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[afurm]

Adding -NonInteractive is correct for preventing prompts in CI, but is this a breaking change for users who relied on stdin input during provisioning? Should there be a config flag to control this behavior rather than always enabling it?

[VedantMadane]

Good point. Adding a config flag makes sense here so existing users who rely on stdin do not break. I can add a non_interactive boolean (default true to match the intent of #12637) so users who need stdin input can set it to false. Would that work for you, or would you prefer the default to be false (opt-in) to avoid any risk?