[electrum] push notification for 5.2.5

Summary:
Notify users of the new release.

Depends on D14147

Test Plan:
./electrum-abc -v --test-release-notification

Go to the Help > Check for updates menu

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14149