Log & Send Events, Improve logging

As of now, markPreemption flag has been set only at the end of the preemption process. There are many other situations to know the current state of preemption for the given request. For example,

1. How many times preemption attempted for the given request and returned before even reaching the end point? Can we log these attempts in allocationLog?
2. Should we send events when checkPremeptionQueueGuarantees check fails?
3. Improve logging, especially debug statements in general