Support leader election when running multiple replicas

[stevehipwell]

Describe the feature
I'd like NTH v2 to use leader election when more than one replica is running.

Is the feature request related to a problem?
I'd like to have multiple replicas running to enable fast switching between the active replica and the standby without waiting for the scheduler.

Describe alternatives you've considered
n/a

[stevehipwell]

If NTH v2 isn't going to replace NTH v1 soon I think this is a requirement for NTH v1 too.

[hajdukda]

Super interested in this - very often happens that the node-termination-handler is scheduled on the node that is currently being terminated and this causes issues.