OplogThread should checkpoint no-op oplog entries

[ShaneHarvey]

OplogThread currently does not update its checkpoint when skipping oplog entries. At best, this leads to re-processing these skipped oplog entries. At worst, the oplog may rollover with skipped entries causing the connector to fail even though no updates that matter happened.

Going even further, we may want to stop filtering out no-ops from our oplog cursor. It's possible that no-ops may cause the oplog checkpoint to rollover too. The majority of the changes would be updating the test suite to pass in the presence of no-ops.