as a user, i'd like the cluster-list data to be clear and easy to skim through.

for clusters that are close to expire, there's a "___ days left" label that shows up under the table's "created" column.

this can be confusing, and is hiding potentially important data (i.e. the "created at" date).

to avoid possible confusion, we need to:

• always show the "created at" date at its column
• when the expiry message is needed, show the alert icon near that text
• move the expiry message (i.e. "___ days left") into a popover, that's attached to the alert icon

(this enhancement was initiated from this slack thread).