[docdb] Better log rotation

Jira Link: DB-2438 Hi

We need a better log rotation policy. 1 way is to keep static naming and allow another process to rotate: https://github.com/google/glog/pull/19 (patch https://github.com/google/glog/commit/58d7f873dcde8cf0fe6f37817643a7ff4e49e6d4)

Another way would be to add an option glog_delete_after and a simple bg thread to enforce the policy. For now, having glog_delete_after=<size> should be a good start. It will take us a day or two to implement and probably save us devops trouble in different environments (k8s sidecar comes to mind).