Make 16.7/7.7 minimum required version to upgrade to 16.8/7.8

Summary

As 16.7 is a confirmed scheduled upgrade stop, marking it as a stop before upgrading any further.

Acceptance criteria

• Attempt to upgrade from any version prior to 16.7/7.7 -> 16.8/7.8 will be prevented and output a suggestion to upgrade to 16.7/7.7 first