[e.cash] add image sharp package

Summary:
I noticed some images are taking a bit long to load, particularly on blog pages.
This package is recomended from next to compliment their image optimization, and hopefully cut down on some load times

Test Plan: preview the site and see if images feel faster

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14306