Adds delay in scale down interval

[vaibhavkhurana2018]

Adds scale down delay interval as an option, with a default value of 1sec.

[ankitjain28may]

• I have tested sqs autoscaler, In this line https://github.com/uswitch/sqs-autoscaler-controller/blob/495f843f28246349704e0adcbaf895bbc909a9c0/pkg/scaler/scaler.go#L74, it should be time.Sleep(s.delay) only as s.delay is in datetime type
• Moreover, I have found that as its a controller running, it keeps on making request to apiserver but because we are doing sleep, it’s also affecting other scaling events for sqs