feat(memory): add internal/external memory separation for multi-channel support

feat(memory): Add internal/external memory separation with RestTemplate client

Description

Summary

• Add multi-channel memory support to distinguish between internal platform users and external channel users
• Replace OkHttp3 with Spring RestTemplate for API Gateway pattern

Changes

MemoryService Interface

• Added getInternalMemory() methods for IAVIA platform users (uses userUuid + agentId)
• Added getExternalMemory() methods for external channels (Slack, Teams, Telegram, WhatsApp) using chatId + channel + agentId
• Removed deprecated getMemory() method

MemoryServiceConstants

• Added INTERNAL_MEMORY_PATH and EXTERNAL_MEMORY_PATH constants
• Added HEADER_CHAT_ID (x-chat-id) and HEADER_CHANNEL (x-channel) header constants
• Added URL builders: buildInternalMemoryUrl(), buildExternalMemoryUrl()
• Removed legacy buildMemoryUrl() and buildMemoryPath() methods

MemoryServiceClient

• Replaced OkHttp3 with Spring RestTemplate
• Implements API Gateway pattern via gatewayUrl + RestTemplate
• Simplified HTTP client with RestTemplate.exchange()

Files Modified

• src/main/java/com/izemx/iavia/common/agent/common/memory/service/MemoryService.java
• src/main/java/com/izemx/iavia/common/agent/common/memory/client/MemoryServiceClient.java
• src/main/java/com/izemx/iavia/common/agent/common/memory/constants/MemoryServiceConstants.java
• CHANGELOG.md

Breaking Changes

• getMemory() method removed - use getInternalMemory() or getExternalMemory() instead
• OkHttp3 dependency removed - now requires RestTemplate bean injection

Test Plan

• Verify internal memory retrieval with userUuid
• Verify external memory retrieval with chatId + channel (SLACK, TEAMS, TELEGRAM)
• Confirm RestTemplate correctly calls API Gateway endpoint /api/memory/**