Migrate Slack Updates to Google Chat via Webhooks

[Krishna41357]

Summary

This PR migrates all Helper App updates (e.g., Knowledge Bank suggestions, Daily Ticket Summary) from Slack to Google Chat using webhooks. Since Slack is no longer in use, all notifications are now routed to Google Chat.

Key Changes

• Introduced a new googleChat folder with a webhook client for Google Chat.
• Updated lib/slack/client.ts to delegate all message-sending logic to Google Chat, preserving the existing API for minimal code disruption.
• No changes required in jobs or other files using postSlackMessage—they now send to Google Chat automatically.
• Added GOOGLE_CHAT_WEBHOOK_URL to .env.local.sample for configuration.
• Slack-specific logic is now stubbed or routed to Google Chat equivalents.

Migration Approach

• Only the slack and googleChat folders were changed; all other files remain untouched.
• Existing integrations and jobs continue to work but now target Google Chat instead of Slack.

How to Test

1. Set your GOOGLE_CHAT_WEBHOOK_URL in your environment.
2. Trigger a Knowledge Bank suggestion or Daily Ticket Summary.
3. Confirm the message appears in your Google Chat space.

Related Issue
Closes #1099