Summary: Issue with k8s HA when the db host and prometheus metrics host are configured as ipv6 loopback addresses the yb_platform_backup.sh script can't handle the surrounding brackets. This diff changes the input argument for hosts to remove any surrounding [] if they exist.

Test Plan:
YBA HA on k8s test
pass in [::1] to backup script ensure db_host is changed to ::1

Reviewers: svarshney, vkumar

Reviewed By: svarshney

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D39741