Update guide - Upgrading Redis OSS to Valkey Cache

[rajlearner17]

Guide to be updated
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In this doc - https://turbot.com/guardrails/docs/guides/hosting-guardrails/updating-stacks/upgrade-to-valkey-cache#upgrading-redis-oss-to-valkey-cache

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  Additionally, AWS has announced that support for Redis in ElastiCache will be deprecated in the future. For more details, see the official AWS announcement.

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  Step 4: Monitor the Update
  Monitor the stack update in progress from the CloudFormation console. Refer Update TED > Step 12: Monitor Update