Make tolerationSeconds field more fine-grained in the failover API

[mszacillo]

What would you like to be added:

I'd like to add an optional initTolerationSeconds to the failover API, so that users of failover can have more fine-grained control of when they'd like to have Karmada trigger failovers.

Why is this needed:

In some cases, we have applications that process large states, and may require some more time to start-up. Since failover only has a tolerationSeconds, this means we must set it to be greater than or equal to the time taken to start up the application.

Ideally, we could have an initTolerationSeconds, which would tell Karmada how long to wait for the application to initialize. After the application transitions to healthy, Karmada would use tolerationSeconds to trigger failover in the case that the application suddenly becomes unhealthy.