[website] Add Korean translation of Avalanche update

Summary: Translation of D11402

Test Plan:
I don't read Korean so relying on the translators.
Also checked google translate to check paragraphs and basic sanity check.
Tested the page locally, translation menu item works.

Reviewers: #bitcoin_abc, Kronkmeister

Reviewed By: #bitcoin_abc, Kronkmeister

Subscribers: Kronkmeister

Differential Revision: https://reviews.bitcoinabc.org/D11406