feat: elasticache and inplace upgrade from redis to valkey

Elasticache/README.md

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+<!-- This readme file is generated with terraform-docs -->
+# Elasticache
+
+Deploy a test redis replication group and then in-place migrate to Valkey
+
+## Migration steps (takes around 17m):
+1. Backup existing instance. Note the version and parameter group
+2. In the example resource below, change apply-immediately, engine, engine-version, and parameter group.
+
+## When redis was initially deployed:
+primary\_endpoint = "lab-cache001.rw4ynm.ng.0001.ape1.cache.amazonaws.com"
+reader\_endpoint = "lab-cache001-ro.rw4ynm.ng.0001.ape1.cache.amazonaws.com"
+
+## After in-place migration to Valkey:
+primary\_endpoint = "lab-cache001.rw4ynm.ng.0001.ape1.cache.amazonaws.com"
+reader\_endpoint = "lab-cache001-ro.rw4ynm.ng.0001.ape1.cache.amazonaws.com"
+
+## Fallback
+Simply reverting the code below will result in a replacement of the replication group. Meaning
+fallback is not supported. One will need to deploy a new instance and restore from backup
+
+## Requirements
+
+| Name | Version |
+|------|---------|
+| terraform | >= 1.11.0 |
+| aws | ~> 6.0 |
+
+## Providers
+
+| Name | Version |
+|------|---------|
+| aws | 6.37.0 |
+
+## Modules
+
+No modules.
+
+## Resources
+
+| Name | Type |
+|------|------|
+| [aws_elasticache_replication_group.example](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/elasticache_replication_group) | resource |
+| [aws_elasticache_subnet_group.subnets](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/elasticache_subnet_group) | resource |
+
+## Inputs
+
+| Name | Description | Type | Default | Required |
+|------|-------------|------|---------|:--------:|
+| application | n/a | `any` | n/a | yes |
+| aws-region | n/a | `any` | n/a | yes |
+| customer-name | n/a | `any` | n/a | yes |
+| environment | n/a | `any` | n/a | yes |
+| owner | n/a | `any` | n/a | yes |
+| project | n/a | `any` | n/a | yes |
+
+## Outputs
+
+| Name | Description |
+|------|-------------|
+| cluster\_endpoint | n/a |
+| primary\_endpoint | n/a |
+| reader\_endpoint | n/a |
+ 
+---
+## Authorship
+This module was developed by xpk.