dfd46ad3fb
This commit adds the upgrade guide for version 2026.1. According to the new upgrade policy, the user can now upgrade to the major version (2026.1) from any previous minor version. So instead of adding a separate guide form 2025.4 to 2026.1, we need a guide from 2025.x to 2026.1. In addition, this commit: - Updates the upgrade policy for reflect the above change. - Removes the upgrade guides for the previous version. Fixes https://github.com/scylladb/scylladb/issues/28533 Fixes https://github.com/scylladb/scylladb/issues/28532 Closes scylladb/scylladb#28789