[s2739] Implement script for Ahune - The Frost Lord

This boss is only active during the Midsummer event

Please note that some visual spells and proc auras, specific to the submerged phase are not yet implemented. They require additional research and core support.

(based on commit 888d0a1)

Signed-off-by: Xfurry <xfurry@scriptdev2.com>