WT-18585 makes a commit timestamp mandatory for writes to disaggregated tables. MongoDB testing shows call sites writing to layered tables without one, so the requirement now defaults to optional (debug_mode=(disagg_commit_ts_optional=true)) and only the WiredTiger test suite enforces it.

The investigation into those call sites is ongoing; details to follow here. Once they are understood and fixed, default the setting back to false and drop the temporary override in test/suite/run.py.