Add types for lifecycle events.

How about the following?

// Lifecycle describes actions that the management system should take in response to container lifecycle
// events.  Management of the container blocks
// until the action is complete, unless the container process fails, in which case the handler is aborted.
// Additionally, for the PreStop handler, the system maintains a timeout, and will automatically terminate the
// container after this timeout, regardless of if the handler has completed or not.  This is necessary for
// the system to maintain its SLA targets. API-initiated terminations may voluntarily reduce this timeout.
...
	// PreStop is called immediately before a container is terminated due to an API request or management event (failed health check, pre-emption, resource contention). The concrete reason and timeout duration are passed to the handler.
	PreStop *Handler `yaml:"preStop,omitempty" json:"preStop,omitempty"`