Graceful shutdown feature

[eldios]

Description

$Customer requested a way to stop Gravity on specific nodes that need to be taken out of commission temporarily for system updates.

The idea is to have a way to stop their application components gracefully or verify if/why/when they didn’t stop cleanly and fix the problem before continuing maintenance.

The desired end goal is having some kind of automated way to just run a simple “one command” that would go through a series of steps and checks to shut down everything cleanly or stop and report if that's not possible.

Internal Design Doc: https://docs.google.com/document/d/13oFa3KbFphyUzmQFJ_cbv1Ley84XWjthmyw3vyIuVaE