LP1809183: Allow passing template to eg-confirm-dialog

LP1809183: Allow passing template to eg-confirm-dialog

Adds an input called dialogBodyTemplate to <eg-confirm-dialog>. This can
be useful when you want to pass ICU messages to <eg-confirm-dialog>
(e.g. "Are you sure you want to cancel these 3 holds?" vs. "Are you sure
you want to cancel this hold?").

If both dialogBody and dialogBodyTemplate are defined, it will show the
dialogBodyTemplate message.

Also adds a sandbox example.

Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>
Signed-off-by: Bill Erickson <berickxx@gmail.com>