[website] Update the upgrade page

Summary: Update the upgrade page with the changes from the next release.

Test Plan:

make serve

Check the upgrade page renders correctly and the content is correct.

Reviewers: #bitcoin_abc, PiRK, Mengerian

Reviewed By: #bitcoin_abc, PiRK, Mengerian

Subscribers: Mengerian, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13250