[e.cash] Add airdrop flag to create wallet button

Summary: Adding an indicator for the new user airdrop now live on cashtab to the landing page "create wallet" button

Test Plan: preview the site and check the landing page

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D16659