[WEBSITE] Fetch documentation in ascending version order

Summary:
This will help speed up the build by better using ccache, and will
prevent issues from old database versions when running bitcoind.

Test Plan:

./script/fetch_documentation.sh

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8705