⚡ (setVariable) Add "Environment name" value in Set variable block (#850)

Closes #848
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
### 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.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/bot-engine/blocks/logic/setVariable/executeSetVariable.ts

@@ -77,9 +77,11 @@ const getExpressionToEvaluate =
   (options: SetVariableBlock['options']): string | null => {
     switch (options.type) {
       case 'Contact name':
-        return state.whatsApp?.contact.name ?? ''
-      case 'Phone number':
-        return `"${state.whatsApp?.contact.phoneNumber}"` ?? ''
+        return state.whatsApp?.contact.name ?? null
+      case 'Phone number': {
+        const phoneNumber = state.whatsApp?.contact.phoneNumber
+        return phoneNumber ? `"${state.whatsApp?.contact.phoneNumber}"` : null
+      }
       case 'Now':
       case 'Today':
         return 'new Date().toISOString()'
@@ -112,6 +114,9 @@ const getExpressionToEvaluate =
         if(now.getHours() >= 18) return 'evening'
         if(now.getHours() >= 22 || now.getHours() < 6) return 'night'`
       }
+      case 'Environment name': {
+        return state.whatsApp ? 'whatsapp' : 'web'
+      }
       case 'Custom':
       case undefined: {
         return options.expressionToEvaluate ?? null