Add WhatsApp Business, Telegram, and Google Chat connector and trigger docs

[VellummyilumVinoth]

Summary

• Add full connector documentation for three new messaging connectors under Connectors > Catalog > Communication: WhatsApp Business, Telegram, and Google Chat, each with overview.md, setup-guide.md, actions.md, triggers.md, and example.md.
• Add corresponding event-trigger integration guides under Develop > Integration Artifacts > Event: whatsapp-business.md, telegram.md, and google-chat.md.
• Wire up the new pages in en/sidebars.ts (Connectors catalog + Develop event section).
• Add supporting screenshots (integration overview, service designer, step configuration/overview) for all three connectors.

It resolves: https://github.com/wso2-enterprise/integration-engineering/issues/2336, https://github.com/wso2-enterprise/integration-engineering/issues/2337, https://github.com/wso2-enterprise/integration-engineering/issues/2338

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