Fix UnicodeDecodeError in WinAdvFirewall on non-English Windows locales

[arielbosquez]

What does this PR do?

WinAdvFirewall.is_enabled() calls subprocess.check_output("netsh advfirewall show currentprofile") and decodes the output with .decode() (defaulting to UTF-8). On Windows systems where the OEM code page is not UTF-8 (e.g. CP850 on Spanish-language Windows), netsh output containing accented characters causes an unhandled UnicodeDecodeError. This crashes the Agent's setup phase before it can begin scanning or propagating — the Agent completes initial recon and reports to the Island, but silently never proceeds past _setup().

Reproduced with:

This PR replaces netsh-based text parsing in is_enabled(), add_firewall_rule(), and remove_firewall_rule() with PowerShell's NetSecurity module (Get-NetFirewallProfile, New-NetFirewallRule, Remove-NetFirewallRule), reading results as structured JSON. PowerShell object property names are locale-independent, unlike netsh's human-readable output, so this fixes the crash for any non-English Windows locale, not just Spanish.

The legacy WinFirewall class (pre-Vista, unreachable on any currently-supported Windows version) received a minimal errors="ignore" safety patch on its own .decode() call, rather than a full rewrite, given its limited relevance today.

No related issue filed prior to this PR.

PR Checklist

• Have you added an explanation of what your changes do and why you'd like to include them?
• Is the TravisCI build passing?
• Was the CHANGELOG.md updated to reflect the changes?
• Was the documentation framework updated to reflect the changes?
• Have you checked that you haven't introduced any duplicate code?

Testing Checklist

• Added relevant unit tests?
• Do all unit tests pass?
• Do all end-to-end tests pass?
• Any other testing performed?

  Tested by running a custom-built Agent (with this fix applied) against a Windows Server with OEM code page 850 (Spanish). Before the fix: Agent completed recon and reported to the Island, then crashed in _setup() with the UnicodeDecodeError above, every time, regardless of how it reached the target machine (SMB propagation, RDP, or manual execution). After the fix: Agent completed network scanning and propagation successfully via both SMB and SSH exploiters, with no errors. Also re-tested against an English-locale Windows Server to confirm no regression.

• If applicable, add screenshots or log transcripts of the feature working