Add WHATSAPP_GROUP_ALLOWED_USERS group allowlist support for WhatsApp gateway

[RiptideV]

What does this PR do?

Adds WHATSAPP_GROUP_ALLOWED_USERS group allowlist support like SIGNAL_GROUP_ALLOWED_USERS

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

How to Test

1. Setup Whatsapp Gateway
2. Add hermes to a group with unauthenticated users
3. Add group to WHATSAPP_GROUP_ALLOWED_USERS
4. Test if hermes responds to unauthenticated users in the group
5. Test that unauthenticated users from the group cannot DM hermes

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform:

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A