BAU: Add snapshot retention window to Redis cache

The snapshot retention window for the AWS::ElastiCache::ReplicationGroup
is 0 by default and therefore not enabled.

This sets the window to 7 days retention so we have data backups and
dynamically sets the SnapshottingClusterId variable to the correct one
in each environment.

copilot/fsd-form-runner-adapter/addons/form-runner-data.yml

@@ -69,6 +69,8 @@ Resources:
         - !GetAtt "FormRunnerAdapterRedisSecurityGroup.GroupId"
       Engine: redis
       NumCacheClusters: 2
+      SnapshotRetentionLimit: 7
+      SnapshottingClusterId: !Sub '${Fn::Select 6, ${Fn::Split ":", ${Fn::GetAtt "FormRunnerAdapterRedisReplicationGroup.ARN"}}}-001'
 
   # Redis endpoint stored in SSM so that other services can retrieve the endpoint.
   FormRunnerAdapterRedisEndpointAddressParam: