[e.cash] Add image optimization size prop throughout

Summary:
Next.js recommends adding a size prop to all images to assist in image optimization. Currently getting a console warning on all images, so adding them here. See docs for reference
https://nextjs.org/docs/pages/api-reference/components/image#sizes

Test Plan: Test site preview and build. Site should look the same, but should have some better image optimizations under the hood, and the console warnings will be gone

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D18532