[e.cash] Add roadmap page

Summary: Adding the roadmap page based on previous content plus roadmap component

Test Plan:
preview the site and navigate to /roadmap
check everything looks good

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman, Fabien, Mengerian

Differential Revision: https://reviews.bitcoinabc.org/D14295