Add temporary file for current release notes page

Summary: This fixes the broken link for the latest release notes when the version has not yet been bumped.

Test Plan:

./scripts/fetch_documentation.sh
make serve

Verify to http://127.0.0.1:4000/doc/release-notes/release-notes-0.22.7.html

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D8442