doc: add skeletons for *_with_timestamp_column (#1220)
doc: add skeletons for *_with_timestamp_column (#1220)

* doc: add skeletons for *_with_timestamp_column

This should unblock our doc writer.

Part of #1217, #1218, #1219

* tidy fixes

* tidy fixes take 2

googleapis/google-cloud-cpp-spanner,googleapis/google-cloud-cpp-spanner,googleapis/google-cloud-cpp-spanner,googleapis/google-cloud-cpp-spanner