Update Backup & Restore External Docs

[tppolkow]

Under Configure an external storage provider in the backup & restore external docs. Let's update

Copy the credentials information from the AWS console to create an IAM credentials file.

to

Provide credentials information to create an IAM credentials file. For testing purposes these can be AWS console credentials like below. For production purposes please provide the credentials to an IAM role with proper permissions ( [link](https://github.com/vmware-tanzu/velero-plugin-for-aws?tab=readme-ov-file#set-permissions-for-velero) )

Or something along these lines. The point is to provide nuance and let the user know these need to be creds to an IAM role with proper permission if they intend to use this option long-term.