Document how to delete a cluster when `cortex cluster down` fails

[vishalbollu]

Description

Create a guide with a checklist of tasks to completely delete the cluster when an error is encountered during cortex cluster down, and link to this guide in the cortex cluster down error message.

Some of the resources to consider:

• cloud formation stacks (mention how you may need to delete resources manually if this fails, starting with the load balancers)
• log groups (optional)
• bucket (optional)
• delete environment
• sqs queues
• api gateway
• cloudwatch dashboard
• vpc link (this probably has to be deleted first)