Migrate Task Queue API and Logs API to GCP clients

[wkurniawan07]

Currently, we use GAE Task Queue API com.google.appengine.api.taskqueue.* and GAE Logs API (com.google.appengine.api.log.*) for queueing tasks and compiling logs. We will change them to their GCP client counterparts, namely Cloud Tasks API and Cloud Logging API.

These two are low hanging fruits in that no additional setups are necessary: creating a GAE app within a GCP project automatically gets them running out of the box.