Add compatibility test for dropDatabase (second pass)

[eerxuan]

Part of #51.

Category: system / changeStreams

Add compatibility test coverage for the dropDatabase feature.

Note: a smoke test exists; comprehensive compatibility test coverage is needed.

[documentdb-triage-tool]

👋 @imforster — this issue has been assigned for 14 days with no activity. Is it still in progress? If you've made progress, please leave a quick update. Otherwise it'll be flagged for re-assignment at the next triage meeting.