Add existing ExponentialBackOff to common project

[liran2000]

Exponential BackOff is a generic use for retry mechanism with backoff and jitter, and commonly used and needed in several applications for multiple different purposes, like failure handling.

Currently, there is an existing implementation for it at com.google.api.client.util.ExponentialBackOff.

Request here is to move, copy or add BackOff interface with the ExponentialBackOff implementation to Guava common project, as many projects do not need http-client dependency, and still want to use Exponential BackOff for multiple purposes which are not related to http client.

http-client depends on Guava anyway.

[ritikBhandari]

hi, Can I work on this issue?

[liran2000]

hi @chaoren

Is it possible to have this issue reviewed by someone, for approving and assigning it ?