Upgrade docs: mention the SOP for minor version upgrades

Currently the upgrade docs on docker-based deployments do not explicitly state which path to follow when upgrading minor versions (e.g. 13.1→13.5), only patch & major versions.

Please provide explicit instructions for minor versions as well going forward.

Since version 8.0, there are no minor version upgrade like 8.0 to 8.1. We don’t release minor versions.