Audit index build lifecycle events

We should indicate when index builds are started, complete, or are aborted. Currently, we only report when index builds are completed.

We should ensure that aborted index builds produce a createIndex event, with the IndexBuildAborted (276) result code.

We should ensure that started index builds produce a createIndex event, with a distinct but identifying result code. We will create a new error code to accommodate this, to be named IndexBuildStarted.