Closes#848
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### Summary by CodeRabbit
- New Feature: Added "Environment name" as a new value type in the
SetVariable function, allowing users to distinguish between 'web' and
'whatsapp' environments.
- Refactor: Simplified session state handling in `resumeWhatsAppFlow.ts`
for improved code clarity.
- Refactor: Updated `startWhatsAppSession.ts` to include an initial
session state with WhatsApp contact and expiry timeout, enhancing
session management.
- Bug Fix: Improved null handling in `executeSetVariable.ts` for
'Contact name' and 'Phone number', preventing potential issues with
falsy values.
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