Add toggle to disable default preStop hook

[nemacysts]

Having a default preStop hook will interfere with upcoming plans to make some of our non-mesh workers gracefully shutdown - this should let us disable this hook per-cluster until we're done (after which, we'll just delete this code entirely) and give us an easy way to rollback without needing to pin paasta-tools back.

[mattmb]

Hmm, maybe this should just be gated behind whether a service is in the mesh or not? Basically if we have the hacheck sidecar then we should have this preStop sleep right? But if not then we shouldn't I think?

[nemacysts]

Hmm, maybe this should just be gated behind whether a service is in the mesh or not? Basically if we have the hacheck sidecar then we should have this preStop sleep right? But if not then we shouldn't I think?

@mattmb oh true - i dunno why I was thinking that the hacheck prestop was good enough! having the hacheck prestop isn't very helpful if the main container has disappeared :p

[mattmb]

Cleaning up and closing some very old PRs. Please re-open or nudge me if you’re still planning to work on this.